The analysis method based on equivalent thermodynamic process is extended to establish a full flow path design method for wide range scramjets. This method is subsequently applied to the design of the full flow path for a wide range scramjet with a variable geometry inlet. Effects of adjustment and combustor size on the engine performance are analyzed. The results show that the inlet mass flow rate has a larger influence weight on thrust than on specific impulse in the range of Mach number 2.0-3.5； thus， best efforts should be made to increase the inlet air flux at the low speed stage. The second compression angle has a larger influence on the engine specific impulse and thrust than the third compression angle. For the given examples in this paper， engine performance benefits from smaller angles of the second compression ramp. The inlet configuration with the optimal thrust is different from that with the optimal specific impulse. The corresponding combustor area also varies dramatically with the flight Mach number if the optimal performance is desired， with higher velocity requiring smaller area. If the high thrust at a lower speed is wanted， the penalties of combustor dimension must be paid at a higher speed， meaning more drag and weight. If high thrust at a higher speed is wanted， the penalties of thrust at lower speeds must be paid， meaning more acceleration time and fuel consumption. This method can rapidly find the flow path scheme with the optimal thrust or specific impulse by comparing massive options， therefore providing strong support for the high performance scramjet preliminary design.