The boundary layer separation frequently happens to compressor blades under the non-design condition. Therefore, through making a slot at the tip region of two blades of a rotor for aspiration, we perform the numerical simulation of the boundary layer suction (BLS) of a double-stage counter-rotational compressor by using the entity slot and adding source terms. Then we make comparative study of the performance characteristics and internal flow field of the compressor before and after aspiration respectively. The study results show that the sucking of low-energy fluid near the rotor tip region can enhance the pressure ratio and efficiency of the compressor under various flow volumes,with its total pressure ratio increasing by about 1.25% and the efficiency increasing by nearly 2%. The flow analysis show that the outlet flow angle at the tip region of the two blades of the rotor is reduced, thus reducing the OGV attack angle and improving the flow of the blade tip region significantly. The pressure ratio prediction results with the source term addition method are close to those with the entity slot method but have a greater prediction efficiency. The reason is that the entity slot method considers the additional loss caused by slot structure.