In the process of flexible assembly tooling design and manufacturing, using the modular design technology can promote the development of aircraft assembly process equipment greatly. The key technology of modular design, namely modular design process, design of special module, universal module design and module interface design were described in detail. According to the instances of flexible assembly tooling design of wall components, the flap flexible assembly tooling, the specific applications of the modular design technology used in the aircraft flexible assembly tooling design were presented. It provides references for the modular based design of the flexible assembly tooling. 