在宜昌九岭头马尾松（Pinus massoniana Lamb.）林中划分25个面积20 m×20 m的标准样地，采用样地调查方法研究了该林分的结构和树种组成特征，并对影响更新幼苗密度的林分结构和树种组成因子进行了分析。结果表明：该林分的乔木层树种共有12科20属21种，乔木平均胸径15.48 cm；各样地中马尾松均为优势种，重要值为21.82%~65.73%。更新层幼苗共有9科11属11种，均为阔叶树，无马尾松更新幼苗，更新幼苗平均密度为1 756 hm^-2。在林分结构变量中，乔木树高为11.74 m，主冠层和下冠层的面积分别为523.74和251.18 m²，主冠层面积与下冠层面积比值（MCA/LCA）为2.91；乔木的胸高断面积、密度和冠幅总面积分别为29.99 m²·hm^-2、1 201.0 hm-2和774.92 m²，草本层盖度为30.53%，林分开敞度为0.24，乔木胸径大小比数为0.45；其中，更新幼苗密度与乔木的胸高断面积、树高、胸径大小比数和主冠层面积呈显著或极显著正相关，与开敞度呈显著负相关。在25个样地中，平均乔木种数为7.7，马尾松和阔叶树的立木比例、胸高断面积、冠幅面积和胸径大小比数分别为44%和56%、23.60和6.39 m²·hm^-2、409.04和365.88 m²、0.26和0.60；更新幼苗密度随乔木种数及马尾松和阔叶树的胸高断面积的增加呈先减小后增大的趋势，均呈二项式关系；更新幼苗密度随马尾松的冠幅面积、立木比例和胸径大小比数的增加而增大，但随阔叶树的冠幅面积和立木比例的增加而减小，均呈线性关系。综合分析结果显示：该林分的垂直结构较为明显，主冠层面积明显大于下冠层面积，但林分内透光条件较差，林木生长空间不足；马尾松个体的胸径较为均匀，但阔叶树个体间的胸径差异较大。影响更新幼苗密度的主要因子为马尾松胸径大小比数和MCA/LCA值以及草本层盖度，以马尾松胸径大小比数的影响效应最为明显。

25 standard plots with area of 20 m×20 m were divided in Pinus massoniana Lamb. forest in Jiulingtou of Yichang City， and stand structure and tree species composition characteristics were studied by using plot survey method， meanwhile， stand structure and tree species composition factors affecting density of regeneration seedling were analyzed. The results show that there are 21 species of trees belonging to 20 genera of 12 families in arbor layer of this stand， and average diameter at breast height of arbor is 15.48 cm； P. massoniana is the dominant species in each plot with important value of 21.82%-65.73%. There are 11 species of seedlings belonging to 11 genera of 9 families in regeneration layer， and all of them are broad-leaved trees without regeneration seedling of P. massoniana， average density of regeneration seedling is 1 756 hm^-2. Among stand structure variables， height of arbor is 11.74 m， areas of main canopy layer and lower canopy layer are 523.74 and 251.18 m²， respectively， and ratio of main canopy area to lower canopy area （MCA/LCA） is 2.91； cross-sectional area at breast height， density， and total canopy area of arbor are 29.99 m²·hm^-2， 1 201.0 hm^-2， and 774.92 m²， respectively， coverage of herb layer is 30.53%， stand open degree is 0.24， and neighborhood comparison of diameter at breast height of arbor is 0.45； in which， density of regeneration seedling shows significant or extremely significant positive correlations with cross-sectional area at breast height， height， neighborhood comparison of diameter at breast height， and main canopy area of arbor， but shows a significant negative correlation with open degree. Among 25 plots， average species number of arbor is 7.7， and proportion of standing tree， cross-sectional area at breast height， canopy area， and neighborhood comparison of diameter at breast height of P. massoniana and broad-leaved trees are 44% and 56%， 23.60 and 6.39 m²·hm^-2， 409.04 and 365.88 m²， and 0.26 and 0.60， respectively； density of regeneration seedling shows a tendency of first decrease and then increase with the increase of species number of arbor and cross-sectional area at breast height of P. massoniana and broad-leaved trees， and both show a binomial relationship； density of regeneration seedling increases with the increase of canopy area， proportion of standing tree， and neighborhood comparison of diameter at breast height of P. massoniana， but decreases with the increase of canopy area and proportion of standing tree of broad-leaved trees， and both show a linear relationship. The comprehensive analysis result shows that vertical structure of this stand is relatively evident， and main canopy area is significantly greater than lower canopy area， but light transmittance in this stand is relatively poor and growth space of trees is limited； diameter at breast height of P. massoniana individuals is relatively even， but differences in diameter at breast height among broad-leaved tree individuals are relatively big. Main factors affecting density of regeneration seedling are neighborhood comparison of diameter at breast height and MCA/LCA value of P. massoniana and coverage of herb layer， and the influential effect of neighborhood comparison of diameter at breast height of P. massoniana is the most evident.