In this work, we use Coherent produced 532nm cw laser as pump source, and 266nm is obtained by frequency doubling. The ring cavity of a laser is generally subject to various perturbation, and the stability of a single-mode laser can be improved by electronically locking its frequency. We use a Pound-Drever-Hall laser frequency stabilization system to control the cavity length. This method utilizes an external phase modulator to produce the sideband and is capable of detecting weak signal to get the information of cavity disturbation. Finally, the signal is dealt with electrical circuit and then feedback to a PZT to control the stabilization of the cavity length.