This paper discusses the research of optimal process for lightguiding plate of backlight module of liquid crystal display. The PMMA material was used on lightguiding plate. This paper indicates that the different processing parameters (mold temperature, injection temperature, first period injection speed, second period injection speed, third period injection speed, packing pressure and packing time) are important for optimal research for lightguiding plate of backlight module. This paper introduces the extension engineering, simulated annealing and genetic algorithm on soft computing for optimal process and compares the results with experiment. The results show that the optimal process group is A1 B1C2 D3 E2 F2 G3 for extension engineering, simulated annealing, genetic algorithm or experiment. The mold temperature is the most important processing parameter of the flatness of lightguiding plate for soft computing and experiment. The calculation times for extension engineering, simulated annealing and genetic algorithm are less than experiment’s time.