Fuel burn is one of the most important parameters in judging the economical efficiency of airplanes. Based on the range equation，main ways to reduce the fuel consumption of airplane have been discussed in this paper. Under the background of conceptual design of an airplane, influence studies of cruise speed, cruise altitude and aspect ratio of wing on the block fuel and the maximum take-off weight (MTOW) have been carried out on the premise of little change in the general layout. According to the findings, general layout optimization and certain developments have been applied to the initial design, and the changes of block fuel, operational empty weight (OEW) and MTOW have been analyzed during the developments. The results indicate that the optimization design brings a 3.92% decrease in the block fuel and a 100 kg reduction in MTOW during the same design range.