In order to solve the problem of fine focus in laser assisted microprocessing, a method of Nd∶YAG frequency doubling is adopted to acquire short wave laser. The frequency doubling in a KTP crystal on Nd∶YAG laser is carried out by the resonant external ring cavity. The maximum average power of Nd∶YAG is 50 W with Q-switch and its frequency is 1005 Hz. A 0.532 μm green light output with 31.4% light conversion efficiency is obtained when the average input power of 1.064 μm laser is 35 W. The proportion of TEM00 model in the green light is 95%. This method is proved to be effective to solve the problem of mini-focus, especially useful in the application of laser rapid prototyping. The experimental results for the characteristics of ring cavity frequency doubling are analyzed and compared with those of 1.064 μm laser on the beam quality.