The quality of aircraft hydraulic transmission line system design is of direct influences on the performance of hydraulic system and user system. In order to form design guide, civil aircraft hydraulic transmission line system design is studied. According to the design thought of civil aircraft, start with requirements, the process and method of hydraulic transmission line system design for civil aircraft each development stage are summarized, including capture of input and output message, use of design method, achieve of design goals. It is very simple and effective to use pressure drop curves to distribute and adjust pressure drop and tubing size. The summarized design process and method in this paper can be a reference for hydraulic transmission line system design for civil aircraft.