This study introduces the accident research system integrated with the medical and engineering network in Japan. Based on the collaborative study by Japan Automobile Research Institute (JARI), Nippon Medical School Chiba Hokuso Hospital and ITARDA (Institute for Traffic Accident Research and Data Analysis), detailed accident data have been collected, and crash, vehicle damage, and injury data were analyzed. This system provides us with the “mechanism” of injury by employing in-depth accident investigation with physical evidence, biomechanical knowledge, and medical knowledge for depicting the injury causation scenario. Moreover, vehicle safety improvement is not the only essential concern for the reduction of road accident casualties and injuries; immediate medical care, such as emergency medical treatment during road accidents, is also necessary. Therefore, the information of emergency medical activities in the post-crash was also collected in this system. This paper introduces the prototype research of the integrated pertinent medical and engineering information and proposes an effective injury-reduction system in actual traffic accidents. The case examples are provided to demonstrate the ability of this system to improve crash /injury assessment. In addition, the accident reconstruction simulation supplements this function of this accident analysis system.