Abstract: Regarding the crane load as a stochastic process, a reliable life assessment method of steel crane structures in service is proposed based on dynamic reliability of fatigue. It can be used to assess the fatigue reliability of steel crane structures in service which may vary with time. In a fatigue reliability point of view, the remaining fatigue life assessment equation in the 《Technical Specification for Inspection, Assessment and Strengthening of Steel Structures》 (YB9257-96) is analyzed, and the probability of the additional safe factor is explained. Then remaining fatigue life of a steel crane structure in service is assessed by the reliable life assessment method and technical specification method, respectively. It is shown that the reliable life assessment method is more reasonable.