On the basis of passivity Q-switch rate equations,the passivity Q-switch output characteristics of Cr4+∶YAG is simulated,and output pulse width and its energy are presented.The laser is designed integrative and has small cubage.The laser works at the repetition rate of 1~40 Hz.The output energy is more than 11 mJ,and the pulse width is 5.2 ns.The jitter of laser is less than 2.5μs.The laser has passed the temperature test of -40~+55℃.