Based on characteristics of driver emergency braking behavior in real traffic scenarios, a new threat assessment algorithm was established for control strategy development of automotive collision avoidance system. Real driving scenarios of drivers in the target area were collected by video drive record (VDR). After manual selection and classification according to the scenario typology defined by National Highway Traffic Safety Administration (NHTSA), six typical types of risk scenarios were obtained. Emergency braking behavior of drivers under these typical risk scenarios were analyzed by using video image processing method and then the tTTC(time to collision) values at the starting point of emergency braking as well as the average values of emergency braking decelerations were obtained. These data were then used to establish the threat assessment algorithm based on 1/tiTTC (tiTTC·tTTC=1) and the required deceleration areq. This threat assessment algorithm can take both the fast closing condition and stable following condition into consideration and correspond with driver emergency braking behavior in real traffic scenarios.