The purpose of this study was to identify how physical injury, perceived threat, forgiveness of others, and problem-focused coping influence the change of posttraumatic stress disorder (PTSD) symptoms. One hundred twenty patients who had experienced a traumatic vehicle accident participated in 1 to 2 months after the accident; 70 of these people involved at 6 months after the accident. We used a hierarchical linear model analysis to verify the impacts of predictors on change of PTSD symptoms as time passed. The results showed that PTSD symptoms decreased over time, and greater perceived threat would worsen PTSD symptoms and more forgiveness would decrease PTSD symptoms. On the other hand problem-focused coping and physical injury severity were not significantly related to the PTSD symptoms. Specifically, greater perceived threat was found to be related with a deceleration of the decrease in PTSD symptoms, whereas greater forgiveness of others was associated with an acceleration of this decrease. However, problem-focused coping and physical injury severity had no influence on the change rate of PTSD symptoms. Cognitive variable could be more important than physical injury to understand PTSD. In addition, forgiveness of other in a traumatic situation needs to be considered as one of coping strategies.