Abstract: In order to discuss the fluctuation law of Apodemus agrarius litter size and the significance for population prediction. We used night trapping method monthly in the paddy fields and dry land to collect specimens of rodents and survey their reproductive status from 1987 to 2012. The result showed that litter size of Apodemus agrarius was 2 to 10 and the average litter size was 5.29. The distribution of litter size was normal distribution with mean 5 or 6, accounting for 35.10% and 33.92% of the total number of pregnant rodents respectively. The majority of litter size was between 4 and 7, accounting for 94.59% of the total number of pregnant rodents. There was no significant difference in litter size between different years. There significant difference in litter size between different months and seasons. Litter size was closely related to population quantity. Litter size directly influences the fluctuation of population quantity. There was significant positive correlation between the average litter size and capture rate, between the average litter size in last year and population quantity in June. We could predicted the occurrence degree of Apodemus agrarius 6 months in advance. Litter size could be used as the reference for population prediction.