Rust causes the static and dynamic characteristics of the steel gate to change， but also changes the reliability of the gate system.In order to study the effect of rust on the reliability of steel gate，this paper analyzes the characteristics of rust based on field detection data，analyzes the stress of arc steel gate support arm by using threedimensional finite factor method，and calculates the reliability of the support arm.The results show that the method proposed in this paper can accurately calculate the reliability of the steel gate support arm to determine the safety of the gate.