Abstract: Seven modules with different axial spacings between two reversed rotating rotors of a counter-rotating compressor were designed,and then the detailed flow structure and performance of them in different rotating speeds was obtained by numerical simulations.The effect of axial spacing on performance of the counter-rotating compressor,inlet flow angle of two rotors and flow structure have been investigated.When the axial spacing between two reversed rotating rotors was changed from 30%C to 70%C,the following observations were obtained:(1)The peak efficiency of counter-rotating compressor decreased approximately 2%,the efficiency of two reversed rotating rotors decreased approximately 4%.(2)At the near stall condition with designed rotating speed,the efficiency and mass flow rate increased firstly and then decreased,and the maximum of the two parameters happened when the axial spacing was 55%C.(3)At the chock condition,the inlet flow angle of the two rotors decreased,contrary to the trend of the chock mass flow rate change.(4)When the axial spacing was bigger than 50%C,it could not affect the inlet flow angle of the two rotors noticeably.(5)Decreasing the axial spacing can improve the performance of the counter-rotating compressor when the loss of mixing is dominating.If the secondary flow loss is the primary loss,increasing the axial spacing is feasible to improve the performance of the counter-rotating compressor.