Condition based maintenance (CBM） promotes the civil aircraft maintenance toward s efficient and economical direction. The concept concerning CBM of broad prospects is elaborated. A CBM decision-making model namely delay time model is introduced, meanwhile, the theory and the modeling process are also researched. Presently, the inspection interval of civil aircraft′s structural component is determined mainly through experience. The delay time model is applied to the decision-making of inspection and replacement of fuselage panel with simulated failure data. The maintence decision-making is optimized with the lowest cost under the costraint of maintence interval. Furthermore, the variation of the optimal interval with different parameters is simulated. The research results verify that the method greatly increases the rationality of maintenance decision-making of components.