Abstract: In this paper, based on the Helmholtz integral equation in a semi-infinite region,the radiated sound field of an arbitrary shaped structure is calculated with Boundary Element Method (BEM). Problems of singular integration, characteristic frequencies, normal noncontinuity at edges and corners, large error in high frequency bands that associated with the using of Boundary Element Method are treated effectively and conveniently. Theoretic numerical calculations are also given to show the high accuracy of these methods.