Abstract：The lateral collision of a car is analyzed in this paper and the strength and design of its deformable barrier and columns are considered. The conditions of the simulation are the same as in the European New Car Assessment Programme (Eruo-NCAP). The influence of the strength and thickness of the door sheet on the safety of the car is discussed and analyzed. The result suggests that the strength and the thickness of the door sheet metal parts are not the key for safety in side impact crash of lateral columns. The central door reinforcement should not be too strong. The door inner panel strength and thickness is the key with respect to the amount of intrusion into the car. This analysis also shows that through the rational distribution of the strength and thickness of the door sheet metal, the door can be lighter by more than 10% as compared with its current weight.