By using a 4-mirror ring cavity and choosing the appropriate direction of the Nd:YAP rod,the laser polarizability and the influence of the thermal effect on laser insidethe cavity have been improved.The single frequency output up to 1.2 W has been obtainedwith the input POwer of 1.2 kW,the fluctuation is less than 2%,and the long termfrequency stability is better than ±0.4 MHz.