In the development of civil aircraft, interface definition work is derived from the functional interface requirements of the system and also serves as input for architecture and lower-level interconnections. It is a critical component in system level, equipment level, and software/hardware level design. The goal of the system interface definition process is to reach a consensus on all interface definitions between this system and other systems. Based on guidelines for civil aircraft and system development, the first step is to clarify the definition and classification of interfaces. Next, focusing on electronic interfaces, the relationship between them and architecture and functions is analyzed, starting with functional analysis to outline the definition process for electronic interfaces. Finally, a hierarchical design approach is proposed, illustrated with a simplified example to explain the forward design steps for electronic interfaces, which can serve as a reference for engineering practice.