In order to analyze the effect of rotor tip jet on the stability enhancement of multistage axial flow compressor, a three-dimensional viscous bulk body force model of axial flow compressor was developed. Through the secondary development of ANSYS CFX software, the N-S equations of momentum and energy source terms were solved, and the full channel numerical simulation of compressor without blades was realized. The error between the pressure ratio characteristics of Stage 35 single-stage compressor calculated based on the model and the experimental data was not greater than 0.8%, and the flow rate at the instability point was 1.2% higher than the experimental value, which could accurately simulate the end wall boundary layer flow. Based on the model, the characteristics and instability boundary of multistage compressor without jet and with jet were calculated, and the mechanism of tip jet expansion was analyzed. The results show that the model can simulate the effect of tip jet on multistage compressor stability expansion. At 100% design rotor speed, the jet flow rate of 4.6% of the design point flow rate enhance the stability margin by 7.06%, and the jet can eliminate the choked flow in the tip area, thus enhancing the stability margin of the compressor.