The paper introduces a kind of miniature laser which is used in Large Games defense system in Beijing.The laser is free of cooling water and uses Cr4+∶YAG as passively Q-switch.Its repetition is 2 Hz and output energy is 20~38 mJ.In order to improve the stability and reliability，Nd∶Ce∶YAG bonded crystal is used as active medium and a pyramid prism is used as the high reflector of the resonator.All of the 50 lasers worked well in the project in spite of the blighted outdoor operation environment in summer.