Crown width and DBH are important tree measurement factors in forest resources survey.Automatic acquisition of crown width and DBH data can improve the efficiency of forest resources investigation.In this study,Pinus yunnanensis was selected as the research object.Based on UAV images,the parameters of individual tree crown width were extracted automatically,and the relationship between crown width,crown area and DBH of different density grade plots was fitted to predict the DBH value of trees.Firstly,the individual tree crown in the canopy height model (CHM) was segmented by marker controlled watershed segmentation algorithm,and the maximum and minimum crown width and crown area were obtained,and the accuracy was evaluated with the mea-sured data.Then,the extracted crown width and crown area were fitted with the measured DBH,and the univariate and binary regression models of each density grade plot were established.The results showed that:the accuracy rate of individual tree crown segmentation was 86.26%,the average relative error of crown width was 6.04%,and the average relative error of crown area was 11.23%;in the fitting model,the fitting effect of crown width & crown area DBH model was the best,the determination coefficient was above 0.7,the relative error of validation data of the model was less than 5%,which met the requirements of class A forest resources survey.The method of extracting crown width and predicting DBH of trees based on UAV image is more accurate,which can provide reference for automatic development of forest resources investigation.