Abstract: The diffracted field of a sound pulse source in a moving stratified medium, in which a shadow zone may be formed, has been studied theoretically. The fundamental equation is reduced to an inhomogeneous linear differential equation of second order by a mixed integral transform, and the solution is expanded into a series of normal modes. Following the method developed by Friedlander, asymptotic expressions of eigen value and eigen functions are derived from Langer's asymptotic solutions. The approximate formula of the field near the diffracted front is obtained for the observing points far inside the shadow boundary. Based on this formula, the establishing process and the attenuation with horizontal distance of field are discussed respectively. These relations are strongly dependent upon the boundary condition and the situations of source and receiver.