The theory and method for generating partially coherent beam based on liquid-crystal spatial light modulator were given. The method was optimized by using partition convolution, the generation of partially coherent beam was parallel sequential optimizied and the generation speed was tested. The coherence width accuracy of partially coherent beam based on double hole interference was detected. Experimental results show that, to a spatial light modulator with a resolution of 256×256, the total time of generating the random phase maps with coherence widths of 0.15mm, 0.9mm and 1.5mm by graphic processing unit are 0.9 ms, 1.75 ms and 2.4 ms, respectively, which are 16.5 ms, 37.8 ms and 52.4 ms by using central processing unit. Considering the reading, sending and response time of the liquid-crystal spatial light modulator by central processing unit, the real-time partially coherent beam generation frequency is up to 312 Hz, which is accelerated by graphic processing unit. For generating a partially coherent laser beam with coherence widths are 0.15 mm and 1.5 mm respectively, the the root-mean-square error are 0.021 306 and 0.020 883, the peak-to-valley are 0.073 576 and 0.072 998.