A fast prediction method based on parabolic equation is presented for the timeliness of the radio wave propagation in large scale partly forested irregular terrain environment. The wide angle Parabolic Equation(PE) method is used, which is solved by Split-Step Fourier Transform(SSFT). In the SSFT step iteration process, the level step is determined dynamically, according to the equivalent dielectric permittivity of forest and irregular terrain. The feasibility and validity of the fast prediction method is verified by simulating the radio propagation characteristic in the partly forested irregular terrain. The results show that the method has higher accuracy compared with the uniform coarse step, and could improve the computational efficiency greatly compared with fine accuracy.