Abstract: The Mixed Effect Model is gradually being applied in the forestry field, which can not only describe the overall change law of data, but also reflect the changes between data, making the estimation results more accurate. Calculating tree height by diameter at breast height provides convenience for forestry investigation to a certain extent. Taking 123 sample plots in Huili City as the research object, the mixed effect model of average height and average DBH of dominant trees in forest stands was constructed, and the correlation between average height and average diameter of dominant trees in forest stands was analyzed. The research results showed that: (1) The correlation between average height and average DBH of dominant trees in forest stands was extremely significant. (2) The fitting effect of the power function model was the best both among individual trees on the whole. (3) The Mixed Effect Model could not only reflect the overall change trend of the average height of dominant trees in forest stands on the average DBH, but also reflect the impact of different tree species. The performance of AIC and BIC was better, and the model fitting effect was better.