Abstract: To address the issue of non-physical reflections at truncated domain boundaries in long-distance computational scenarios for the parabolic equation wave propagation model, this paper proposes an improved adaptive absorbing window method based on angular spectrum regulation. First, the angular spectrum domain is analyzed to examine the spectral energy leakage phenomenon of the standard absorbing window in long-distance propagation calculations. Subsequently, an angular spectrum leakage correction model based on exponentiation is proposed. By employing a dynamic parameter optimization strategy, the standard deviation of the angular spectrum at each iterative step is analyzed to establish a dynamic matching mechanism between the absorbing window parameters and angular spectrum characteristics, enabling adaptive parameter adjustment to control spectral leakage. Comparative simulations with the standard absorbing window validate the effectiveness and superiority of the proposed improved absorbing window across various scenarios. Finally, the method is applied to solve the problem of electromagnetic wave propagation in a three-dimensional atmospheric duct environment. Simulation results indicate that, compared to the domain expansion method, the proposed improved absorbing window significantly enhances computational accuracy, providing a novel approach to improving computational efficiency in large-area parabolic equation solutions.