A high energy ultraviolet laser is studied. High quality fundamental frequency laser of high quality is generated through diffuse-refective cavity, varied reflectivitymirror (VRM) unstable resonator and electro-op tic (E2O) Q-switching. With 5Hz repetition rate, ultraviolet light pulse energy of 140mJ /pulse at 355nm is achieved using phase-match of type Ⅱ for KTP and phase-match of type Ⅱ for LBO, that the divergency angle is 1. 5mrad, and the beam diameter is 6. 5mm.