Through investigating the growth of middle age of Pinus massiana forest, the genetic variation of population was analyzed. The result showed there were abundant genetic variation and very significant or significant differences among families of Pinus massiana in height, diameter breast-high, volume and crown, moreover, the differences were mainly controlled by genetic factors and these growth traits were genetically controlled in medium or lower level. Principal components analysis showed that height, diameter breast-high, volume and crown were principal components, the cumulative proportion of these three principal components achieved 89.54%. Using software Structure Version 2.2 to analyze the genetic structure of population, all families were divided into 5 groups. The group 4, including most families of Guangdong, had the most growth traits. The group 2, including most families of Guangxi, the growth traits was next to that of the group 4.