Abstract: To study the optimal diameter structure of natural forests of Cupressus funebris in the northeastern edge mountains of Sichuan,37 standard plots of Cupressus funebris natural forests in the northeastern edge mountains of Sichuan were selected as the research objects.The plots were divided into five intervals based on the hectare volume,ranging from small to large.The average Q values when the forest stand's average growth was maximum from 2002 to 2017 were calculated for each interval.Subsequently,the negative exponential distribution model,linear model,and power function model were employed to fit the optimal diameter structure of Cupressus funebris natural forests.The results showed that within the five volume classes of 22.7~38.4 m³/hm²,45.8~74.7m³/hm²,80.7~100.8 m³/hm²,107.5~132.8 m³/hm² and 136.4~147.0 m³/hm²,the average growth reached its maximum in the volume class of 107.5~132.8 m³/hm²,with an average growth of 28.8 m³/hm² and an average Q value of 1.7 during the period from 2002 to 2017.Among the three models used for fitting the optimal diameter structure,the negative exponential distribution model yielded better results with an R-squared value of 0.852.Quantifying the optimal forest diameter structure provides theoretical support and technical methods for the future management of natural forests in the region,where Cupressus funebris is the dominant tree species.