In forested ecosystems, complex forest canopies may redistribute and chemically modify the composition of rain water; this field within the study of ecological hydrology has recently attracted a considerable amount of attention. Throughfall is a major part of the rainfall penetrating the forest canopy and redistributes rainfall, and throughfall patterns can affect the distribution of soil water as well as the cycling and use of nutrients. Furthermore, spatial variability in the amount of throughfall can affect the concentration and deposition of solutes and the spatial distribution of nutrients in a forested landscape. Therefore, changes in throughfall beneath the canopy have very important effects on water balance, hydrological processes, and nutrient cycling within forest ecosystems. Many studies have analyzed the effects of the forest canopy on the interception and redistribution of rainfall, and the regularity of throughfall in different forest types; these studies provide a clearer understanding of the hydrological processes involved in rainfall interception and redistribution. However, few studies have addressed the horizontal spatial distribution of throughfall under a forest canopy. An examination of the spatial distribution of throughfall would provide important data to aid comprehension of the eco-hydrological processes and nutrient cycling within a forest. The goal of the present study was to determine the spatial heterogeneity of throughfall under a forest canopy and to explore the ecological mechanisms of the effects of canopy structure in a Larix gmelinii forest on throughfall. Several factors, such as distance (of the sampling site to the trunk), canopy thickness, and leaf area index (LAI), can all influence the spatial distribution of throughfall. Throughfall was measured under a Larix gmelinii forest canopy at three locations-beneath the canopy itself, beneath the canopy edge, and in canopy gaps-during 19 rainfall events, using 38 rain gauges during the period of development of a stable canopy (Jul.-Aug. 2013). The spatial heterogeneity of both forest canopy structure (LAI and canopy thickness) and throughfall were analyzed using statistical methods. The spatial variability of throughfall in the Larix gmelinii forest analyzed here was estimated for different rainfall events. The results indicate that throughfall under a Larix gmelinii forest canopy was 148.33 mm during the observation period, and accounts for 80.62% of the rainfall in an open field. The throughfall ratio increased with increasing amounts of rainfall, and the relationship between these could be described with a power function (P<0.01). The coefficient of variance of throughfall decreased with increasing rainfall amounts, and the relationship between these could be described with a logarithmic function (P<0.01). Structural characteristics of the canopy were found to be the most important factors controlling the spatial variability of throughfall, and the throughfall amount was significantly negatively correlated with the degree of complexity within the canopy structure (P<0.01). The influence of distance was most important, and was significantly positively correlated with the throughfall ratio (r²=0.580, P<0.01). Canopy thickness and LAI were significantly negatively correlated with the throughfall ratio (P<0.01), but exhibited poor fitting results. When considering the ecological mechanism of throughfall, canopy thickness was the most important canopy structure/factor that affects the spatial redistribution of throughfall in a Larix gmelinii forest.