Li Chengqian
It is not known when Li Shizhi was born, but it is known that his grandfather was Li Chengqian, the eldest son and original crown prince of Tang Dynasty's second emperor Emperor Taizong. Li Chengqian was deposed in 643 but spared, and his line was bypassed in the subsequent succession, which eventually went to his brother Li Zhi (Emperor Gaozong). Li Shizhi's father Li Xiang () served as a prefectural secretary general during the reign of Emperor Gaozong's wife Wu Zetian, but was removed by her. Li Shizhi himself started his public service as an officer of the imperial guards during the second reign of Emperor Gaozong's son (and thus his cousin) Emperor Zhongzong.