Abstract: In order to study traffic safety and efficiency at upstream functional areas of unsignalized intersections, the decision-making process and its influential factors of driving behaviors before entering into intersections are studied. The data is collected by video in Nanjing,China.The speed and deceleration of decelerating driving behaviors are extrac-ted,and their features are quantitatively analyzed.A variance analysis method is used to estimate the degree of influence of each influential factors on the speed and deceleration,and a model of driving behaviors between deceleration and influ-ential factors is developed.The results show that,the speed of vehicles has an obvious downtrend at upstream functional areas of unsignalized intersections,and speed distribution gradually changes from discrete to centralize.The changing process of vehicles'deceleration is from large to small.The initial speed (V A0 )and left/right steering rotation angle are selected,and have significant effects on the model.The study provides constructive suggestions and theoretical basis to improve intersection design,traffic policy and the safety.