Understanding the mechanism and process of community assembly is a key issue in ecological research. Functional traits, which represent plant physiological, morphological, and phenological attributes, have decisive effects on plant growth, survival, reproduction and dispersal. Examining the spatial distribution pattern of plant functional traits and its response to local environmental variation is helpful to speculate the underlying processes and mechanisms that regulate community assembly. In this study, we explored the underlying mechanisms of community assembly using the dataset from a 21.12hm² temperate conifer and broad-leaved mixed forest plot in Jiaohe, Northeast China. Four topographic attributes, including elevation, convexity, slope, and aspect, were measured as local environmental factors. Six functional traits, namely leaf area, specific leaf area, leaf carbon content, leaf nitrogen content, leaf carbon to nitrogen ratio, and maximum tree height, were collected and measured for all 34 woody species that present in this temperate forest plot. Two functional structure indices, including the mean pair-wise trait distance (PW) and the mean nearest neighbor trait distance (NN), were used to explore the spatial distribution pattern of plant traits. Furthermore, regression analyses were used to investigate the response of trait patterns to environmental variation. Based on the results of PW, we found that, except for the leaf area traits, the remaining traits mainly showed the clumped spatial patterns. The results based on NN showed that, except for the leaf area and maximum tree height, the remaining traits presented the clumped spatial patterns. The results of regression analyses showed that the distribution patterns of functional traits were significantly affected by elevation, slope, and aspect. In contrast, convexity had no significant effect on trait distribution in this temperate forest community. Our results indicate that the non-random processes including environmental filtering and biological interactions played important roles in regulating forest community assembly, while the role of neutral process was not significant in this temperate conifer and broad-leaved mixed forest.