Based on the in-depth accident study of 138 cases occurred in Shanghai, China, in which a passenger car got side impact, the characteristics of human - vehicle/equipment - environment factors were analyzed in order to reveal the causation and damage/casualty consequence of these side impact accidents. The results show that the average deformation of these side struck passenger cars was 22.4cm. Furthermore, the deformations caused by large striking vehicles (trucks and buses) were 52% larger and the ratio of critical casualty consequence (serious injury or death) hovered at 22%. On the other hand, the highest mortality occurred at both sides of rear seats, and was nearly 13%. The head and neck were the most prominent injured parts of the body, which occupied narrowly 64% of the casualties. These above objective characteristics of side impact accidents provide a reliable basis for the development and application of occupant protection system and collision avoidance technology in China.