Abstract: Passively Q-switched Cr4+∶YAG/Nd∶YAG all-solid-state infrared laser,pumped by a diode laser,was designed.Then with a lens of 100mm focal length focusing the 1064nm IR laser to a 9mm KTP second-harmonic generation crystal,a green laser pulse was obtained with average output power of 29mW.At last,with a lens of 30mm focal length focusing the 532nm green laser to a 4mm length of BBO fourth-harmonic generation crystal,an ultraviolet laser pulse at 266nm was obtained with peak power of 7.3W,average output power of 1.1mW,repetition rate of 12.5kHz,pulse duration of 12ns.Ratio of green-ultraviolet power conversion is 3.8%,and that of infrared-ultraviolet power conversion is 0.7%.