By comparing the differences between the development goals of military and civil aircraft projects, it was pointed out that the ultimate goal of civil aircraft projects was to pursue commercial success. By comparing the proportion of investment in each phase of civil aircraft project, it was emphasized that the predevelopment phase played a vital role in setting the project tone, indicating the development direction and reducing the development risk. It was concluded that the two tasks of the predevelopment phase were aircraft definition and conceptual scheme iteration & optimization. The work content of the predevelopment phase was divided into three stages: market analysis and aircraft definition, feasibility study and preliminary design. The relationship of each stage, internal workflow and practice were described. It was pointed out that the output of market analysis and aircraft definition stage were presented in the aircraft definition documents and determined by the aircraft definition review meeting. The focus of feasibility study stage was the expansion and iteration of the scheme, in which the market verification was an vital reference for scheme optimization. And the preliminary design stage should give continuous attention to the market verification and advanced technology research. Finally, the market orientation, scientificity and the essentials of investment in the predevelopment phase of civil aircraft were summarized.