Abstract: Forest soil is one of the main carbon pools in terrestrial ecosystem. Its organic matter content can provide basic information for estimating soil carbon storage, and also, is an important index for evaluating the function of soil carbon sink. Based on the LiDAR data and the topsoil organic matter contents in 55 permanent plots at Liangshui National Nature Reserve, Heilongjiang Province of Northeast China in August 2009, and by using partial least squares (PLS) method, this paper retrieved the forest topsoil organic matter’s spatial pattern in the Reserve, extracted and screened the variables related to the distribution of the topsoil organic matter (e.g., intensity, counts, elevation, slope, and aspect), and analyzed and defined the correlations between the screened variables and topsoil organic matter content, with the prediction model of forest soil organic matter content established and validated. In the Reserve, the forest topsoil organic matter content was significantly and positively correlated with three variables (intensity, r=0.765; counts, r=0.423; and elevation r=0.475; all P<0.001). The model prediction on the topsoil organic matter content was reliable (precision=83.3%, R²=0.725, RMSE=1.955). In the areas of forest edge and of low canopy stands, the topsoil organic matter content was less than 100 g·kg^-1. The majority of the study area had a topsoil organic matter content of 100-150 g·kg^-1, while a few areas had the topsoil organic matter content as high as 150-318.4 g·kg^-1.