Tree diameter structure is an important and basic role in forest structure. For the reason that the diameter at breast height (DBH) can be easily and accurately measured. Because it has a close relationship with variables such as stand density, tree age, tree height, canopy, biodiversity and so on, diameter structure is often used as a direct-response stand structure characteristic. DBH belongs to a set of non-spatial forest structure factors, and is frequently used to analyze the relationship between stand structure and growth, e.g. Recently, studies of forest spatial structure have expanded, partly due to the fact that the DBH is an important factor in explaining the growth of trees, and in many cases because the diameter structure has been used to analyze the relationship between spatial structure and DBH. Similarly, DBH is also an important factor in reflecting the growth of moso bamboo (Phyllpstachys edulis) forests. The DBH of moso bamboo can directly influence leaf area and root area volume, which affects the growth of moso bamboo. Others have performed a number of research studies on the relationship between DBH and other bamboo forest structure factors, such as bamboo height, age composition, canopy structure, and so on. However, these factors are generally measures of non-spatial structure. Recently, research suggests that a distance-dependent spatial index can accurately describe the moso bamboo stand structure, and therefore it is important to analyze and control the relationship between moso bamboo stand structure and function. Previous studies rarely reported the relationship between moso bamboo stand spatial structure and diameter. Therefore, three spatial structure parameters, uniform angle index, neighborhood comparison and age mingling degree were used to analyze the relationship between moso bamboo spatial structure and diameter, and thus provide a theoretical basis for sustainable moso bamboo forest management. The study was established in a close-to nature moso bamboo stand in Tianmu Mountain National Nature Reserve, Zhejiang province. The study design involved a fixed plot of 1hm² (100 m×100 m), which was divided into 100 units by adjacent grid inventory. Each moso bamboo was located in terms of x-, y-, and z-coordinates using a Total Station. Three spatial structure parameters, including neighborhood comparison, uniform angle index, age mingling degree were evaluated. The DBH was recorded into one of three classes: Ⅰclass (DBH < 7 cm), Ⅱ class (7 cm ≤ DBH < 13 cm), Ⅲ class (DBH ≥ 13 cm). These classes were used to analyzed the relationship between spatial structure and DBH of the close-to-nature moso bamboo stand. The results showed that the frequency distribution of DBH had a right-skewed normal distribution, which is the similar to even-aged arbor stands. The spatial pattern of class Ⅱand class Ⅲ was of random distribution, similar to the distribution of the whole stand, but the pattern of class Ⅰshowed an aggregation distribution pattern. The uniform angle indexes decreased with increasing diameter classes, and results showed that the uniform index had a powerful relationship with DBH, with the determination coefficient between DBH and uniform index being 0.7793. The uniform angle of different diameter classes showed no obvious significant difference (P > 0.05). The neighborhood comparison showed that for stands in an intermediate status, the DBH differentiation was not significant. The neighborhood comparison values showed that the ranking of the dominant degree was: Ⅲ > Ⅱ > Ⅰ. And the neighborhood comparisons decreased with increasing diameter classes, as well as had a significantly linear correlation with DBH (the determination coefficient was 0.9233). The neighborhood comparison of different diameter classes showed significant differences (P < 0.01). The average age mingling of the stand was 0.8178, suggesting the age mingling intensity was intensive. The age mingling values showed the ranking of age segregation was: Ⅲ > Ⅱ > Ⅰ. And age mingling increased with increasing diameter classes, as well as had a strong relationship with DBH, where the determination coefficient was 0.6774. The age mingling of different diameter classes was also significanly different (P < 0.01).