Species of Microtus fortis, are always associated with rivers, flooded areas and wetland, and it is considered a good swimmer. To understand the adaptability of M. fortis to the aquatic movement, we observed and tested their swimming behavior, waterproof property of fur and ability in the laboratory and got the following results: M. fortis was able to swim on the water and underwater, but mainly swimed on the surface (Fig. 1), their swimming speed was about 0.37 m/s. The propulsion in water was maximized through a drag-based paddling motion. Their fur was waterproof that not only providing buoyancy, but also supporting they swimming longer time. They could swim as long as 5 h at 20 ℃ in this study. The waterproof quality of their fur was better in females than in males (P < 0.05), therefore female owned a bettter swimming ability (P < 0.05, Fig. 3). The long-term swimming ability of the vole is mainly determined by its fur waterproof performance (P < 0.01, R2 = 0.682, Table 3). At the same time, the resistance of fur to water had a negative correlation with their age and weight (P < 0.01, R2 = 0.805, Table 3). These results indicated M. fortis has well-waterproof fur and excellent long-term swimming ability. This species has evaluated adaptation to the aquatic movement.