Based on the Finite Element Analysis Method, the running safety of light rail train on long span double deck cable- stayed bridge is evaluated. The total element and nodes amount of the refined 3D couple vibration finite element model, which the bridge is made up of main truss, cable, tower, piers, cap, piles, and soil and the light rail vehicles include the car body, bogie, wheel-set, and spring-damp system, is over 2.2 million. The model is solved on Dawning 4000A supercomputer of Shanghai Supercomputer Center based on the Contact Balance Bisection (CBB) algorithm for parallel computing and the vertical and transverse wheel-rail interaction force are obtained. According to the derailment coefficient and the wheel load reduction rate under maximum velocity, the running safety of light rail train is analyzed, which provides the reference for the safety design of long span cable-stayed bridge.