One of the most important things in developing aircraft structure maintenance program is to determine the inspection task and intervals for structure accidental damage. Given the lack of using datum, the method of using rough set and case based reasoning (CBR) is introduced to civil aircraft MSG-3 analysis. According to the requirement of civil aircraft MSG-3 (Maintenance steering group) analysis, the research into the method of civil aircraft MSG-3 analysis using CBR is conducted and key techniques, including the case base development, case representation, case retrieval, maintenance task and interval determination, are investigated. Meanwhile, to avoid human’s subjectivity influence, rough set is used to allocate the weight of the MSG-3 analysis factors. Finally，we use the significant structure item of aircraft as an example to verify the method.