Due to the diversity of landforms, an appropriate threshold should be selected for the simplification of different landforms. The distribution of simplified index was obtained by preprocessing the terrain data, and the distribution was used as a reference for threshold selection. In order to study the influence of terrain simplification on the prediction of complex electromagnetic environment, a visibility algorithm used in the regular model of terrain and a probability-based power propagation model are proposed. The visibility algorithm used in the regular model of terrain is based on the relationship between planes and triangular planes in three-dimensional space. The visible triangular surfaces and the corresponding visible area of the triangular surfaces in the terrain can be calculated with the visibility algorithm. The probability-based power propagation model uses the results of the visibility algorithm to calculate the propagation probability and calculates the change of receiver power in combination with the radio wave propagation characteristics. The spatial visibility algorithm and the probability-based power propagation model can be applied to the complex electromagnetic environment to analyze the influence of terrain simplification on prediction accuracy. The minimum error between the experimental result of the probability-based power propagation model and the Wireless InSite simulation result is 0.5018dB, and the average error is 1.5039dB.