In order to find out population composition and population fluctuation law of Eothenomys melanogaster and provide scientific basis for control, the systematic monitoring results of rat situation in Kaili City, Guizhou Province from 1984 to 2012 were analyzed. The analysis results showed that the Eothenomys melanogaster mainly distribute in the paddyfield and dryland, accounting for 6.60% of the total quantity. It’s one of the common rat kinds in local. The average capture rate in paddyfield and dryland was 0.42%. There was significant difference in population between different months. There were 2 population peaks in May to June and September to November within a year. The average capture rate were 0.50%-0.53% and 0.43%-0.54%, respectively. The peak presented a typical bimodal curve. Population quantity showed difference in different years and different seasons. Population quantity seasonal variation also showed difference in different regions. April and August was the best control period.