Abstract: We analyzed the weight of 3059 samples of Rattus norvegicus (1573 female, 1486 male) which were captured in Yuqing, Xifeng, Dafang, Sandu and Guanling County in Guizhou provience from 1986 to 2008. The average body weight was 108.30±49.00g，There was no significant variation in weight by sex. According to the frequency distribution of weight, the Rattus norvegicus were divided into 5 age groups. The weight division standard for each age group was determined: Juvenile (≤60.0g), Sub-adult (60.1~110.0g), Adult Ⅰ(110.1~160.0g), Adult Ⅱ(160.1~210.0g), Old-adult(>210.0g). There is significant variation in population reproductive capacity in different age groups. Population reproductive capacity of Rattus norvegicus would increase continuously with growth within age categories. Adult group I, group II and the old group were the main reproductive contributors. The research shows that the average pregnancy rate, mean litter size and average descent rate of testicle were 46.60%, 7.00and 91.49%, respectively. There is significant seasonal variation in the population age structure. The population age structure changes were almost the same.