Abstract: Observation was conducted to analyze influence of Matsucoccus sinensis Chen.upon the height growth of Pinus yunnanensis.It was showed by the results that the height growth was not influenced when the population density of Matsucoccus sinensis Chen.was under 5 heads per bundle of needles.The height growth was reduced when there were more than 5 heads of pests per bundle of needle leaves, and the reduction quantity increased when the pest population increased above the density, and the loss of height growth of Pinus yunnanensis differed significantly from site conditions and the pest densities.The infection severity of Pinus yunnanensis stands by the Matsucoccus sinensis Chen.pest was classified into 4 categories i.e., healthy, slightly, intermediately and heavily infected based on statistical analysis.