In this paper, the far-field aerodynamic noise of coaxial counter rotating propeller was predicted by combining the rapid prediction theory of aerodynamic noise and the rapid prediction method of aerodynamic load. The influence of BWI radiation efficiency on the main control of BWI interference noise of coaxial counter rotating propeller was analyzed. The counter rotating propeller with equal number of front and rear blades from low to high (single row 6-12) was studied. The results show that although the aerodynamic noise characteristics are different between low blade number and high blade number, the high sound pressure region at front and behind region is still dominated by BWI noise. At the same time, the design of equal blades number only makes the high sound pressure region more concentrated, but it can not be reduced. It is considered that non-equal blade number CRPs have better acoustics performance than equal one after the comparison between several non-equal configurations. The matching scheme is obtained for the number of blades before and after CRPs with same total blade numbers. High accuracy method will be used to study the nearfield acoustic in the future to get more characteristic of radiation efficiency.