According to the automobile industry has been developing day by day, traffic accidents are increasing and the rear-end collision is the second largest of the entire collision. Due to the high social cost caused by rear-end collision, several studies are in progress at home and abroad. Previous studies have shown that neck injury caused by rear-end collisions can be prevented by seat conditions. In this study, to find the condition that reduces neck injury, change of neck injury in rear-end collision is analyzed according to headrest height, seatback angle, and seatback torque using BioRID II dummy model and passenger behavior analysis program MADYMO. Therefore, it is expected that the condition of each variable to reduce the risk of injury to the neck can be applied to the seat design, which will reduce the injury and the social cost caused by the rear-end collision.