A high power end-pumped Nd:YVO4 all-solid-state ultraviolet (UV) laser was demonstrated under acousto-optic Q-switched operation, using type Ⅰ phase-matched LiB3O5 (LBO) as second harmonic generation (SHG) crystal and type Ⅱ phase-matched LBO as third harmonic generation (THG) crystal. To improve the optical to optical (O-O) efficiency of fundamental wave to THG UV laser, a concave reflection mirror is used to focus the laser into THG LBO crystal, which avoids the chromatic aberration of traditional focusing lens effectively. Finally, the output power of 355 nm UV laser reaches to 1.86 W at the incident pump power of 23.3 W, and the output power of fundamental wave is about 7.28 W at 20 kHz repetition rate, and O-O conversion efficiency is about 25.5% accordingly. The test results of UV laser beam quality indicate that the laser can still work at a good beam quality even at the maximum output, which means that the UV laser can have a very good beam quality even at the high power output.