In the present study, steady air injection upstream of the tip blade leading edge was studied. To reveal the mechanism, steady numerical simulations were performed on a transonic axial compressor, NASA rotor 37. The injection angle α is 20° and three injector axial position were studied, respectively 9, 18 and 27% upstream of the axial chord length at blade tip (ca). For each position a different injection mass flow rate and different injection yaw angles were simulated. The results show at design speed (n =17188 r/min), with injector position at 9% ca, injection mass flow rate of 2% and injection yaw angle between -20° and -30°, the mass flow rate at stall can decrease for approximately 3%, but others compressor parameters were affected such as the total pressure ratio. With injector positioned at 27% ca, the decrease in the mass flow rate at stall is less obvious, but the effect on the compressor pressure ratio is benefic.