The invention discloses a contact network failure risk assessment method based on a binary decision graph algorithm, comprising the steps of: (1) generating a BDD structure, determining system boundaries, basic events and top events, establishing and normalizing a fault tree, and generating a BDD structure, wherein the corresponding BDD nodes may be directly created by ITE operations for basic events; and ITE operations may be performed on basic events or other intermediate events to obtain the BDD structure of the original intermediate event for intermediate events; (2) calculating the accident rate of the contact network failure risk, generating a Boolean logic expression by the fault tree, and generating a Boolean logic function corresponding to the fault tree top event, wherein when the true value is obtained, the probability of occurrence of the top event or any intermediate event may be obtained; and (3) measuring the event importance. The invention applies the BDD method to thefailure risk assessment of the contact network, which simplifies the calculation process, and solves the problems such as the combined explosion and the complicated solving process encountered by thecut set method in the contact network failure fault tree analysis.