A novel approach is proposed to design an aircraft heat exchanger considering multiple working conditions to develop the conventional approach that designs for only one working condition. Calculation results show that the performance of the heat exchangers designed by this novel approach meets the requirement of pressure drop and heat transfer for all working conditions (flight height varies from 0 m to 12,000 m, and Mach number varies from 0 to 1.2). After working conditions discrete and heat exchanger design, the extreme working conditions of pressure drop and heat transfer rate are found not coincided, which have been all considered in design without artificially screening. Therefore, it is not necessary to find a ‘seeming extreme working condition’ before design for this approach. In the optimization design, a deeply optimized structure of heat exchanger is proposed by changing the values of the selected structural parameters to reduce by roughly 30% of the total weight in comparison to common design results. Moreover, the pressure drop and the heat transfer rate of the optimal result can be reasonably distributed at different working conditions. Actually in this novel approach, more other specific criteria required could be also added into the integrate criterion of optimization to control the result. In addition, two detailed optimization methods, sacrifice of secondary objective parameters and ‘the macro-to-micro design method’, have been proposed in optimization design for further optimal structure.