Abstract: In this paper the formulas for the estimation of sound pressure amplitude at the point receiver behind a half-infinite sound barrier,especially in the"shadow"region are given.The barrier may be a thin screen,or a wedge,or a wide barrier.These formulas are based on the Huygens-Fresnel's principle of diffraction and obtained directly on the concept of Fresnel half-period zone.Using these formulas a new method called Fresnel Zone Method 10 calculate sound insertion loss of a barrier is obtained.The calculations agree well with experimental results.