Abstract: Quantity criterion and compartmentalizing measure of car following regime were not put forward because of lacking time serial car following data.After reviewing the research of car following models, the various compartmentalizing car following regimes and key parameters for the same model were deducted in this paper, then the unite car following model that reflects driver behavior and vehicle run characteristic in fact traffic flow is established.196 000 pairs of car following data of fact traffic flow in Beijing expressway were collected, and 208 time segments data were selected, that include only one regime car following data in every time segment.Dynamic gathering measure of average acceleration of time segment car following data was taken to compartmentalize full car following process to three regimes, such as acceleration regime, stabilization regime and deceleration regime.