The parabolic equation (PE) method which deduced from the wave equation is the most precise one for predicting the radio propagation in troposphere, whereas the traditional algorithms only forecast forward-propagating waves but neglect backward-propagating waves giving rise to more error in the presence of irregular terrain boundary environment. Thus, in this paper, the recursive two-way parabolic equation modelling and its in-depth procedure is presented which can compute the forward propagation and backward propagation field over any irregular terrain enhance the computation accuracy and remedy the insufficiencies. Compared to traditional WAPE and GTD, the correctness and applicability of the model are verified by simulation results in the normal atmosphere over single knife-edge and couple triangles.