To effectively and efficiently reduce injuries at traffic accidents, analyzing human body's dynamic response and head-neck injury in relation to considerations of men's safety are a relevant task. In order to reduce human injury severity through better automobile design, to analyze the dynamic response and injury of occupant in collisions are important before we develop the protection devices of car occupants. The purpose of this study is to explore rear-end crash phenomena by using MSC/DYTRAN finite element code. The dynamic response and neck injuries of occupant under crash is discussed using FMVSS standard. Additionally, it also considers the effects of the protection devices on reducing the neck injury. These results can be useful for evaluation of crash safety of a vehicle and design of new occupant restrain devices.