The research investigated the main distribution areas of the population of Acer catalpifolium, a precious and endangering plant in Sichuan Province, and analyzed the relationship between the diameter structure and the intraspecific and interspecific competition of the population, and explored the relationship about competition intensity, diameter and distance. The results show: (1) there is a significant power function relationship between A. catalpifolium diameter and height. The diameter class structure of the population is normally distributed. There are many trees at middle and small diameters and fewer trees at higher and higher diameters. (2) The intraspecific and interspecific competition intensity of the A. catalpifolium accounting for 15.16% and 84.84% of the total competition intensity (222.87), respectively, indicating that the competition mainly comes from the interspecies. (3) The competition intensity between A. catalpifolium and its main associated species was in order of Cryptomeria fortunei > Phoebe zhennan > Quercus fabri > Kalopanax septemlobus > Bothrocaryum controversum > Betula platyphylla > Cunninghamia lanceolata > Magnolia officinalis > Betula luminifera. The target trees and competitors distance and competition index are well subject to the exponential function relationship; When the distance between the target trees and competitors is less than 1 m, the competition index can reach 5.5; with the gradual increase of the distance, its competition index decrease accordingly and eventually tends to be flat. (4) The competition intensity decreased with the increase of the diameter of the target. When the diameter of the target is less than 20 cm, the competition pressure is the greatest, and the competition index is the largest among the A. catalpifolium and the entire forest (234.98) and the A. catalpifolium and interspecific (184.01); When the target diameter is less than 10 cm, the competition index can reach 18; when the target diameter is larger than 20 cm, the competition intensity changes little and the competition index is lower; the competition intensity and the target trees diameter obey the power function relationship (CI=AD^-B). (5) The model prediction results show that with the increase of the A. catalpifolium diameter, the competition index is getting smaller and smaller, and the competition intensity is decreasing. When the A. catalpifolium diameter is 0 to 5 cm, the competition intensity between A. catalpifolium and the entire forest is the highest, and the competition index was 7.14, accounting for 50% of the total competition intensity. When the diameter is greater than 20 cm, the competition index has changed little. This model can predict perfectly the intraspecific and interspecific competition intensity of A. catalpifolium.