A deep ultraviolet solid-state laser system using nonlinear optical frequency conversion technique, which is based on sum-frequency generation in a CLBO crystal is reported. The two beams involved in the sum-frequency generation are 1064 nm from an all-solid-state acoustic-optic Q-switched Nd:YVO4 laser and 238.7 nm from a third-harmonic generation of a Tisapphire laser pumped by a lamp-pumped electronic-optic Q-switched frequency-doubled Nd:YAG laser. The Q-switched frequency-doubled Nd:YAG laser, Tisapphire laser, BBO third-harmonic generator, Q-switched Nd:YVO4 laser and CLBO sum-frequency generator in the system are described in detail. Stable 195 nm deep ultraviolet laser with maximum output power of 217 μW at 10 Hz is achieved in experiment.