A compact and highly efficient green-light source is demonstrated based on periodically poled Mg:LiNbO3 (PPMgLN) crystal. The MgO:LiNbO3 samples of 1 mm thick, 6.95 μm domain period, uniform periodicity, near 50% duty cycle are fabricated by use of a high-voltage multi-pulse poling method. A maximum power of 3.8 W at 532 nm is obtained by a 6.8 W laser diode (LD) pumped, the PPMgLN length in Nd:YVO4 intracvity is only 1 mm, and the corresponding optical to optical conversion efficiency is 56%.