Abstract: On the basis of the data of the central regions of Beijing,through researching and analyzing the causes leading to the crashes of vulnerable road users, and considering the characteristics of the vulnerable road users,the concept of the movable obstacles in sight was used firstly and it provided a new solution to the prevention of crashes of vulnerable road users.To asses the frequency and severity of traffic crashes,the concept of crash severity and indexes of conflict severity are proposed.At the same time,a model for predicting crash severity is established and it is helpful to predicting and estimating the situation of the traffic safety of the vulnerable road users.