Abstract: A modified shooting and bouncing beam method is proposed in this paper, which can calculate the acoustic scattering field of circular trihedral corner reflector quickly. A lot of discrete points are selected on the arc edge of circular trihedral corner reflector. The adjacent two discrete points plus the vertex of corner reflector form a planar element, and the planar element together with the sound source position form an incident sound beam. The reflection of each sound beam is calculated based on geometrical acoustic method; at the same time, the new planar element forms after getting the "radiation" of each sound beam on the reflecting surface. The acoustic scattering field of every planar element is calculated based on physical acoustic method. The superposition of all planar elements' scattering fields is the corner reflector's scattering field. The comparison between the results of the original shooting and bouncing beam method and the modified one shows that the two calculations are consistent. However, the modified shooting and bouncing beam method decreases the computational complexity greatly.