In order to solve the interference problem of the accelerating pedal and the front floor, and to improve the ride comfort and safety, a 3DCS assembly variation analysis model was built. Running Monte-Carlo visual assembly, the probability distribution of the analysis target and the sensitivity analysis result of contributors were obtained, and then, a robust optimization for datum layout of the accelerating pedal and the mounting panel was presented. The significant Geo-Factor, quality loss level and failure rate of assembly quality of the accelerating pedal between the original design and the robust optimization design was analyzed and compared, and the probability distribution image of assembly quality was drawn to verify the availability of robust optimization. Robust optimization based on the assembly variation analysis result can improve the efficiency of robust optimization design, and the product quality can meet design requirements.