During his reign, he destroyed the rival Former Qin and proceeded to expand his hegemony over nearly all of western China, as he temporarily seized all of Western Qin's territory and forced Southern Liang, Northern Liang, Western Liáng, and Qiao Zong's Western Shu (西蜀) all to at least nominally submit to him, but late in his reign, defeats on the battlefield, particularly at the hands of the rebel general Helian Bobo (who founded Xia), and internecine struggles between his sons and nephews greatly damaged the Later Qin state, and it was destroyed soon after his death.
Yao Xing was an avid Buddhist, and it was during his reign that Buddhism first received official state support in China.
For the next several years, as Yao Chang fought with Former Qin and Western Yan, Yao Xing was often entrusted with guarding the base of operations (initially Beidi (北地, in modern Tongchuan, Shaanxi), later Chang'an after Western Yan captured and then abandoned it), while his father engaged in campaigns.
He was considered to be firm and gracious, and he spent much time studying literature despite the work necessary in maintaining home base.
Yao Xing was able to stop Fu Deng's attack on Dou fairly easily.
Despite Yao Xing's hopes of keeping his father's death a secret, Fu Deng received news of it anyway—and immediately prepared a major attack against Later Qin.
Yao Xing set up his army at Mawei (馬嵬, in modern Xianyang, Shaanxi) to prevent Former Qin forces from reaching the river near Mawei, and Former Qin forces were stricken by thirst, but still fought harder.
Yao Xing initially ordered Yin to be cautious, but Yin, realizing the trouble the Former Qin forces were already in and believing that morale would be destroyed if he undertook a cautious strategy, fought back fervently, and the Former Qin forces collapsed.
As Fu Deng sought to join up with Qifu Yizhou, Yao Xing ambushed and captured him, and then executed him.
Yao Xing was described to be in such great mourning that he was unable to handle matters of state for some time.
Overall, during this period, Yao Xing was described by historians as diligent and willing to listen to different opinions, ruling the empire efficiently.
In 399, Yao Xing sent his brother Yao Chóng the Duke of Qi and the general Yang Fosong (楊佛嵩) to attack the important Jin city of Luoyang, and in winter 399 captured Luoyang and the surrounding cities.
Qifu Gangui himself surrendered to Southern Liang's king Tufa Lilugu, thus temporarily ending Western Qin's existence.
In fall 400, believing that he was being suspected by Tufa Lilugu, Qifu Gangui fled from Southern Liang and surrendered to Later Qin.
Yao Xing created him the Marquess of Guiyi and, in 401, took the unusual action of giving Qifu Gangui his army back and ordering him to defend his old capital Wanchuan (苑川, in modern Baiyin, Gansu), and while Qifu Gangui was in name a Later Qin general, he acted independently at times.
To avoid conflict, Tufa Lilugu ordered Southern Liang forces to yield a path for Later Qin forces, and Yao Shuode therefore easily reached the Later Liang capital Guzang (姑臧, in modern Wuwei, Gansu), putting the city under siege.
In summer 402, Yao Xing personally led a major attack against Northern Wei, which had by this point taken over nearly all of Later Yan's territory north of the Yellow River.
Around this time, Yao Xing also appeared to have become a devout Buddhist, under the influence of the monk Kumarajiva.
The Later Qin general Liu Bobo (who would later change his name to Helian Bobo), who was then in charge of Shuofang (朔方, in modern Ordos, Inner Mongolia), because his father Liu Weichen (劉衛辰) had been killed by Northern Wei forces in 391, became angry and declared a rebellion, establishing Xia.
Also in 407, Qiao Zong, who had taken control of Jin's Yi Province (modern Chongqing and Sichuan) and declared himself the King of Chengdu, became a Later Qin vassal.
In 408, noticing that Southern Liang was under severe attack by its neighbors (including having suffered a terrible defeat to Xia in 407), Yao Xing launched a campaign to try to destroy Southern Liang, despite opposition by his official Wei Zong (韋宗), who felt that Tufa Rutan would not be defeated easily.
He commissioned his son Yao Bi (姚弼) the Duke of Guangping along with Qifu Gangui and Lian Cheng (斂成) to attack Southern Liang, while simultaneously commission Qi Nan (齊難) to attack Xia.
Around this time, there also began to be increasing tendencies by Yao Xing's brothers and sons to plot to take over power.
Later in 409, the Jin general Liu Yu launched a major attack on Southern Yan, which sought aid from Later Qin.
In 413, Liu Yu's general Zhu Lingshi (朱齡石) attacked Qiao Zong's Western Shu state and destroyed it, reannexing it to Jin.
In summer 415, the Jin general Sima Xiuzhi (司馬休之), having been forced to escape after Liu Yu attacked him, fled to Later Qin.