【Objective】 This study aims to assess the simulation accuracy of two measures of understory beam radiation: the scaled weighted beam shading degree and the weighted inside-boundary neighbor beam shading degree. These measures are part of a forest understory radiation simulation system based on easy measurable tree factors. The study also seeks to identify model structural characteristics using these simple, measurable tree factors to provide a reasonable and accurate estimate of beam radiation at any understory location. 【Method】A stand pixel model was established using broadleaf Pinus koraiensis (Korean pine) forest stand survey information and it simulated the understory beam transmittance. This transmittance served as a benchmark to evaluate the scaled weighted beam shading degree and the weighted inside-boundary neighbor beam shading degree. Various parameters for these degrees were optimized using a hill-climbing algorithm. The simulation performance of these measures was assessed by comparing the proportions of beam radiation transmitted through gaps, using Pearson and Spearman correlation coefficients and linear regression determination coefficients between understory beam transmittance and the two degrees under the optimized parameters.【Result】The results indicate that the scaled weighted beam shading degree provided the best linear regression fit for understory beam transmittance in the broadleaf Korean pine forest, with a neighbor tree selection minimum scale (r_min) of 6.332 m and a maximum scale (r_max) of 13.609 m. The Pearson and Spearman correlation coefficients, as well as the linear regression determination coefficient between this measure and understory beam transmittance, were -0.581, -0.645 and 0.338, respectively. By contrast, the weighted inside-boundary neighbor beam shading degree showed a linear regression fit for understory beam transmittance, with a neighbor tree selection maximum threshold (T_max) of 1.965 and a minimum threshold (T_min) of 0.502. The Pearson and Spearman correlation coefficients, as well as the linear regression determination coefficient for this measure, were -0.738, -0.695, and 0.545, respectively. 【Conclusion】(1) Both the scaled weighted beam shading degree and the weighted inside-boundary neighbor beam shading degree effectively reflect the understory beam radiation, with the latter performing better. (2) When constructing a simulation model of beam radiation in forests based on tree factors, it is crucial to select neighboring trees that influence beam radiation and to seek a straightforward method to accurately represent beam radiation at various times.