During the brief reign of his grandnephew Zhang Zuo, he was honored as Prince Cheng of Liang (涼成王).
In 320, the magician Liu Hong (劉弘), who had spread rumors that the gods wished for him to be the ruler of Liang Province, convinced two of Zhang Shi's guards Yan She (閻涉) and Zhao Ang (趙卬) to assassinate Zhang Shi.
In 322, Zhang Mao had his general Han Pu (韓璞) seize the Longxi (隴西) and Nan'an (南安, together roughly modern Dingxi, Gansu) Commanderies – which appeared to be then under nominal Han-Zhao control, while Han forces were battling the rebel Chen An, extending his domain east of the Yellow River.
However, in 323, after the Han emperor Liu Yao defeated Chen An, he continued on and reached the Yellow River, claiming to be ready to cross it.
Zhang went into a battle posture, but negotiated peace, agreeing to submit to Han authority and offering tributes of horses, livestock, and jewels.