Abstract: This study was conducted to determine phenotypic variation of Acer mono Maxim at different altitude and found out the relationship between phenotypic variation and microenvironment in Shanxi. We used nested analysis，principal component analysis, correlation analysis, cluster analysis，variance analysis and multi-comparison to analyze the 22 phenotypic traits for 200 individuals in 7 populations of Acer mono Maxim. The results showed that there were significantly differences in genetic variation in phenotypic traits. Mean phenotypic differentiation coefficient among populations was 42.61%. Coefficient of variation of 22 phenotypic traits varied from 7.98% to 33.41%. Shannon-Wiener information index and Simpson genetic diversity index was 2.0164 and 0.8316 respectively，and which showed that there was high phenotypic diversity in Acer mono Maxim. Principal component analysis showed that the four principal components added up to 94.39% of the variation，among which the contribution rate of cone and leaf were higher than that of seed. A significant relationship had occurred between phenotypic traits and some soil factors，like potassium（K），phosphorus（P），potential of hydrogen（pH），indicating the influence of microenvironment of different altitude populations on phenotypic traits of Acer mono Maxim phenotypic diversity index also had a very significant correlation with soil factors. The Acer mono Maxim investigated could be divided into two groups according to the cluster analysis.

Key words: Acer mono Maxim., phenotypic diversity, population