He became emperor after his violent and impulsive nephew Liu Ziye was assassinated in January 466, as he was regarded as more lenient and open-minded at first.
For reasons unknown, Wen once wanted to put her to death, but she convinced him that killing her would offend the spirit of his deceased wife, Empress Yuan Qigui, and she was spared.
Emperor Xiaowu posthumously honored Liu Yu's mother Consort Shen as Princess Dowager of Xiangdong, and Emperor Xiaowu's mother Empress Dowager Lu Huinan took over the duties of raising Liu Yu to adulthood.
Emperor Qianfei was impulsive and violent, and he, after discovering and brutally suppressing a plot to depose him in favor of his granduncle Liu Yigong (劉義恭) the Prince of Jiangxia, suspected his uncles as well, and had them returned to the capital and confined.
(Another even older uncle, Liu Hui (劉褘) the Prince of Donghai, was considered so unintelligent that Emperor Qianfei did not view him as much of a threat.)
One of the nephews that he tried to promote, Liu Zixun the Prince of Jin'an, whose chief of staff Deng Wan (鄧琬) had just prior to Emperor Qianfei's death declared a rebellion against Emperor Qianfei, refused, and instead declared a rebellion against Emperor Ming, in association with Yuan Yi (袁顗) the governor of Yong Province (雍州, modern northwestern Hubei and southwestern Henan) and Liu Zisui's chief of staff Xun Bianzhi (荀卞之).
However, Liu Zixun's generals proceeded slowly, believing that Jiankang would collapse on its own due to the lack of food supply.
Liu Hu fled back to Xunyang, but then left under guise that he was going to set up perimeter defenses while instead fleeing.
Instead of his initial policy of pardoning those who had declared for Liu Zixun, he began to deal with those who had not surrendered by this point harshly.
Late in 466, Emperor Ming created his oldest son, Liu Yu (different character than his own name), crown prince.
He was joined in this action by Bi Zhongjing (畢眾敬) the governor of Yan Province (兗州, modern western Shandong), Shen Wenxiu (沈文秀) the governor of Qing Province (青州, modern central and eastern Shandong), and Cui Daogu (崔道固) the governor of Ji Province (冀州, modern northwestern Shandong), although Shen and Cui soon changed their allegiance back to Emperor Ming.
With Ji and Qing Provinces now completely isolated from the rest of Liu Song, they could not be supplied with fresh troops, and the Northern Wei general Murong Baiyao (慕容白曜) forced Cui's surrender in spring 468 and captured Shen Wenxiu's defense post at Dongyang (東陽, in modern Weifang, Shandong), annexing those provinces for Northern Wei.
(While Pengcheng would temporarily be taken by Emperor Wu of Liang, the rest of the territory was lost to Southern Dynasties forever.)
Also on one occasion, he held an imperial feast inside the palace, and ordered his ladies in waiting to strip for the guests.
Whoever violated these taboos would be executed, often in cruel manners, including having their hearts cut open or their entrails pulled out.
In 471, Emperor Ming grew ill, and as Crown Prince Yu was only eight, he was fearful that his brothers would seize the throne, and therefore turned against them.
His first target was Liu Xiuyou the Prince of Jinping, who was considered arrogant and violent and often offended Emperor Ming.
The only brother who was spared with Liu Xiufan (劉休範) the Prince of Guiyang, who was considered to be unvirtuous and incompetent, and therefore not viewed as a threat.