Abstract: Grazing angles obtained by ray tracing(RT) have nothing to do with wave length, and may give multi-values or none in some areas. The plane wavefronts assumption of plane wave spectral estimation (PWS) violates the characters of wave propagation in inhomogeneous atmosphere. A parabolic equation model (PE) model based on the cured wave spectral estimation (CWS) is proposed for the wave propagation computation on rough sea surface. Grazing angles are estimated with the CWS from the PE outcomes on smooth surface, and then PE on rough surface can perform with them. With the new method, grazing angle can be uniquely obtained at arbitrary distances, avoiding the paradox of a chicken-and-egg problem. Performances of RT, PWS and CWS are simulated and analyzed. Performances and feasibility of the new method is checked on rough surface PE with numerical experiments.