Abstract: By use of the materials and data registered from 1962-1964 and 1979-1980 the age structure and nature renewal of the population of Apodemus agrarius in the suburbs of Shanghai were analysised.The seasonal fluctuation of population density may be drawn with a curve of double peaks, being higher in fall season, so that it may also be called"posterior peak type'', manifesting the character of subtropical seasonal dynamics. There are two breeding peaks yearly and there is a interval of breeding diapause of 3-4 months in winter.The reproductivity of population increases with that the mean age of individuls in population. The rate of fecundity and number of embryos are prominently influenced by seasonal ambient temperature. Those individuls produced at the interval of summer and autumu, being mature in 5-7 months, will be the main strength of breeding in following spring. Sex of those individuals which produced in spring come to maturity only in two months. Almost the main party of them cannot tide over the bitter cold in winter and will die off thoroughly.From these point of view, it may be recognized that the population of Apodemus agrarius renews once a year.In winter, numbers of Apodemus agrarius in pupolation continually decrease. At that very period, a good opportunity may be taken for eliminating wintering individuals and reducing rodent calamity in next year.Yellow weasals are natural enemies of Apodemus agrarius and should be better protected.