It is reported that the slot of microcutting Si wafer by second and third harmonic output of YAG laser is narrower in water bath than in air environment. The surface morphology and etching rate for water bath and air environment are compared in detail. The cutting gap as small as 10 μm with edge fluctuation less than 5 μm is obtained in water bath by 355 nm laser. This technology may be helpful for industrial applications.