:A passively Q - switched laser which is not cooled by water using Cr4 + YAG as saturable absorber with pulse repetition frequency 10Hz and output energy 100mJ is presented. Several types of laser without water cool are analyzed. In order to improve the performance of the laser ,a pyramid prism is used as high reflector of the resonator.The output energy per pulse is 107mJ ,112mJ and 103mJ at the room temperature , + 50 ℃amd - 40 ℃respectively.