Abstract: The variation law of the population reproduction characteristic of different age groups of Apodemus agrarius in Yuqing County, Guizhou Province, have been studied and analyzed systematically from 1999 to 2004. 1011 Apodemus agrarius(including 483 female and 528 male) have been dissected during study. There are distinct age variation in the sex ratio of the population of Apodemus agrarius and obvious discrepancy in the population reproduction capacity of different age groups. The population reproduction capacity increases continuously with the growth of the population age. Adulthood Group I, dulthood Group II and Old Age Group are reproductive population of Apodemus agrarius, and their average pregnancy rate is 45.97%, each birth deliver 5.02 young, testicular dropping rate is 91.98% and reproduction index is 1.0618. Average pregnancy rate, testicular dropping rate and reproduction index are 1.57, 1.42, 1.52 time of and obviously higher than that in the mass except that the difference between the average numbers delivered in each birth and in the mass is not remarkable. How much is the proportion of the three groups are in the population is closely to the decrease or increase of the populations, and which can be regarded as an important basis to predict the population number of the Apodemus agrarius.