The characteristics of 355 nm ultraviolet (UV) nanosecond (ns) laser generation using third harmonic generation (THG) method based on the new nonlinear optical (NLO) crystal Na3La9O3(BO3)8(NLBO) were investigated. A Q-switched high-power 1 064 nm laser with repetition frequency of 10 kHz and pulse width of 10 ns was applied as the fundamental laser source. A type I phase-matched LBO crystal was used for the second harmonic generation (SHG) and a type I phase-matched NLBO crystal was used for the THG. The output power of 355 nm UV laser is 152.5 mW, and this is the highest output power of 355 nm UV laser generated by NLBO crystal. The variation of the crystal deflection angle with temperature when the NLBO crystal achieved the optimal THG output was studied, and the optimum phase matching angles at different temperatures were modified.