Aimed at the complicated structure and remarkable rigidity of the process of flight line maintenance, a process optimization method based on modular theory is proposed. According to the theory of modular evolvement, the modular trend of flight line maintenance is demonstrated. The programming course and symbol description of modular process is educed. Process activities are identified by work break down structure. The association among maintenance activities is depicted by combining with graph structure model，and a reasonable maintenance module k-division is realized by the optimization algorithm of DSM model. The process optimization model of small outfield/big infield maintenance is educed from a quantitative view. Finally, a new method of resource optimization and flexibility improvement is established.