Based on field investigations and analysis of the distributions of Acer mono Maxim, 19 populations were sampled to provide insights into the variation trends, distribution patterns, mechanisms, and adaption of 23 phenotypic traits by variance analysis, relevance analysis, and the UPGMA cluster analysis. The results showed the following: (1) there were significant differences between 20 phenotypic traits among and within populations except for FSL(Fruit stalk length), BTM (Bears the mark), SLW(The ratio seed length to width). (2) The average value of coefficient of variation (CV) was 18. 07, and the trend of CV was as follows: fruit (19.78%) > leaf (18.77%) > seed (10.25%). (3) The mean phenotypic differentiation coefficient VST of populations was 50.66%. The variation among populations (48.82%) was approximately equal to that within populations (51.18%). The order of VST was leaf (58.08%) > fruit (41.24%) > seed (25.87%). (4) The trend of the Shannon-Wiener index H was leaf (6.1079) > fruit (5.9118) > seed (5.2855), and that of the Simpson index D was fruit (0.9967) > leaf (0.9961) > seed (0.9948). (5) Principal component analysis (PCA) showed that the main variation sources of A. mono was leaf > fruit > seed. (6) The phenotypic trait variations of A. mono populations were affected by longitude and latitude in spatial distributions. There was significant correlation between some traits and the longitude/latitude. (7) The 19 populations of A. mono clustered into 2 groups according to the UPGMA cluster analysis. High phenotypic diversity occurred in the A. mono populations. Together these results provide a foundation for the preservation and utilization of A. mono.