Liquid crystal spatial light modulator (SLM) is an effective method to improve spatial beam quality. A shaped iterative algorithm of spatial light intensity is proposed. The spatial non-uniform of the back-stage laser system with 50 m transmission distance is compensated in the complex high-power solid-state laser system by using a small-aperture liquid crystal SLM of the front stage. Experimental results show that nearfield beam quality can be improved by using SLM. After spatial beam shaping, the output nearfield modulation is 1.26:1, the fluence contrast value is 5.1%, the soft-edge factor is 8.1% and the nearfield similarity to the target beam is 99.83%.