The characteristics of static pressure changing at stage exits of a multi-stage axial flow compressor relative to the design points at several typical operating modes are investigated. On low-to-mid operating conditions, the pressure change at the rear compressor stages caused by engine operating mode transition is not as sensitive as that at the front compressor stages, so it's hard to detect compressor instability precursory signals through the conventional method of monitoring the flow parameters at compressor exit. Then, to improve the efficiency of compressor instability precursory signal detection, it's necessary to install sensors on the front compressor stages, which would be useful for the detection of imminent compressor instabilities at low-to-mid rotating speeds of engine.