In order to solve the problem that the rencent design method can only fit the small divergence angle situation, a novel method is prensented for disigning the beam laser splitter with large angle based on the Rayleigh-Sommerfeld Integral. In the design, firstly the target intensity distribution is modified with coordinate transformation and intensity adjustment, then the modified Gerchberg-Saxton algorithm is adopted to optimize the phase distribution of the beam laser splitter. Our method and original method are used to design the 5×5 splitter with 40°×40° diffraction angle. The simulation and experiment result shows that original method shows significant pillow distortion and uneven intensity distribution. In contrast, the sub beams of the splitter designed by our method are well-proportioned and the intensity distribution is even.