A continuous-wave(CW) 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd:YVO4 and using LBO as the intra-cavity SHG crystal.With the optimization of laser cavity and crystal parameters,the laser operates at a very high efficiency.When the pumping power is about 31 W,the output at 457 nm reaches 4.2 W,and the optical to optical conversion efficiency is about 13.5% accordingly.The stability of the output power is better than 1.2% for 8 h continuously working.