There have been few researches on the reliability of prestressed steel structure, especially the study on the reliability considering the failure of key components. In order to study the impact of the component failure on the structure reliability, the response surface method based on central composite design is adopted and APDL language is applied to write a corresponding program, thereby carrying out reliability calculation and analysis to the model. The system reliability and parameters sensitivity of the beam string structure under different failure of components are provided. The results indicate that the impact of cable failure on the reliability is large, but it is weak by the failure of brace rod. The results may serve as a reference for the health monitoring and safety assessment of the prestressed steel structure.