Abstract: Analyzing the concept and the function of the ratio of rotation speed difference in a twin-spool turbojet engine indicates that the ratio has an effect on the surge margins of the high and low pressure compressors and the match between the speed of high pressure compressor and the inlet gas temperature. It is proposed how to adjust the ratio of rotation speed difference reasonably. The results of the adjustments made by us are shown in good agreement with the trial run data. In addition, the effects of the ratio on the thrust, specific fuel consumption, speed of high pressure compressor and turbine inlet gas temperature are also considered.