Near the end of the Tianbao era, as he was a capable archer, he came to serve under the Tang general An Lushan, and made contributions in defeating Tujue tribes.
After Yan ended with Shi Chaoyi's death in 763, Zhang Zhongzhi surrendered to Tang, was bestowed the name Li Baochen, and became a Tang general — the military governor (Jiedushi) of Chengde Circuit (成德, headquartered in modern Shijiazhuang, Hebei), and Zhang Alao served under Li Baochen.
[2] While serving under Li Baochen, Zhang Alao was given a number of honorary positions, and a new name of Xiaozhong (meaning "filially pious and faithful").
In 775, when Tian Chengsi, then the military governor of Weibo Circuit (魏博, headquartered in modern Handan, Hebei) wore out the patience of not only the imperial government by annexing most of Zhaoyi Circuit (昭義, then headquartered in modern Anyang, Henan), killing Li Baochen's brother Li Baozheng (李寶正), and being disrespectful to Li Zhengji the military governor of Pinglu Circuit (平盧, headquartered in modern Weifang, Shandong), Emperor Xuanzong's grandson Emperor Daizong commissioned a campaign against Tian.
[2] Subsequently, when Li Baochen was tricked by Tian into attacking another general, Zhu Tao, the acting military governor of Lulong Circuit (盧龍, headquartered in modern Beijing) but was unable to seize Lulong Circuit, Li Baochen made Zhang the prefect of Yi Prefecture as precaution of a Zhu counterattack.
This is just like how you, Lord, do not go to pay homage to the emperor.Zhang Xiaojie protested that if he returned with this message that Li Baochen would surely kill him, but Zhang Xiaozhong pointed out that if they went back together, they would both die, but if he did not go, Li Baochen would not dare to act against Zhang Xiaojie — prediction that turned out to be correct.
Zhu wanted to continue on to the capital of Chengde, Heng Prefecture, but stopped his advances when, to his surprise, Zhang backed off and withdrew to Yifeng (義豐, in modern Baoding).
When his subordinates questioned this move, Zhang stated his reasons:[6] There are still many experienced officers at Heng Prefecture, and we should not take them lightly.
[6] After the victory at Chengde, however, Emperor Dezong made a series of moves that simultaneously alienated Zhu and Wang.
Zhu was angered by Emperor Dezong's refusal to give him any part of Chengde territory (in particular, Shen Prefecture) and requiring him to capture two additional prefectures on his own, while Wang was angered that contrary to Emperor Dezong's implicit promises to give whoever killed Li Weiyue Li Weiyue's offices, he not only received a lesser title, but was in a position where he could easily be destroyed.
Subsequently, when Wang Wujun sent Wang Shizhen to put Kang under siege at Zhao Prefecture (趙州, in modern Shijiazhuang), the imperial general Li Sheng, whose forces had been part of the forces fighting against Tian in the south, requested leave to advance north to meet Zhang to relieve Zhao Prefecture, and Emperor Dezong agreed.
This, however, drew a response from Zhu, who left Tian's capital Wei Prefecture (魏州) and arrived at Qingyuan to battle Li Sheng.
[8] In fall 783, troops from Jingyuan Circuit (涇原, headquartered in modern Pingliang, Gansu), then at Chang'an to wait for deployment to the eastern battlefield, mutinied when Emperor Dezong did not give them sufficient rewards, forcing Emperor Dezong to flee to Fengtian (奉天, in modern Xianyang, Shaanxi).
In spring 784, after Emperor Dezong tried to quell various rebellions by issuing a general pardon, he gave Zhang the honorary chancellor designation of Tong Zhongshu Menxia Pingzhangshi (同中書門下平章事).
[9] In 786, after the realm had become relatively peaceful and submissive to Emperor Dezong's authority again, there was a famine for the region north of the Yellow River.