The highway guardrail is the last secure defense which can protect the driver and passenger safety and make the vehicles along the original correct direction when out of control. Collision simulation between vehicle and semi-rigid waveform beam guardrail was achieved. Collision model was given and dimension optimization of the semi-rigid waveform beam guardrail was completed. Dynamic explicit finite element method was applied to simulate and analyze collision process. Optimized height of the lower beam and thickness of the upper and lower beams were obtained, which helped save material, solve the tripping phenomenon and increase safety property of the highway guardrail.