To study the distribution pattern and changing mechanism of small mammals in the Dongting Lake from the perspective of animals using water to migrate and diffuse, we captured 13 adult Striped Field Mouse (Apodemus agrarius) and 11 adult Grey Shrew (Crocidura attenuata) in the Dongting Lake area for swimming tests at the end of July 2018, observed their swimming behavior, and measured their fur absorption of water for 3 minutes, 5 minutes, 10 minutes, and 30 minutes. The data were analyzed using repeated measures analysis of variance. The results showed that: (1) The Grey Shrew use the horizontal dog-paddle posture during swimming and stroke water with all limbs (Fig.1), which the water absorption rate of fur increased with the swimming time but there was no gender difference (P > 0.05, Table 1). (2) The Striped Field Mouse, who use the horizontal dog-paddle posture during swimming, mainly use hindlegs to draw water and can float with no paddle (Fig.2), and the water absorption rate of fur increased with the swimming time with no gender difference (P > 0.05, Table 2). (3) The waterproofness of the fur between the two mammals was significantly different (P < 0.05, Table 3): the water absorption rate of Grey Shrew was 12.7%, 18.22%, 26.31% and 26.46% respectively, and that of Striped Field Mouse was 9.16%, 12.41%, 13.87% and 15.90% respectively (Table 3); the water absorption growth rate of Grey Shrew was 4.232%/min, 1.105%/min, 0.809%/min, 0.005%/min, and that of Striped Field Mouse was 3.054%/min, 0.650%/min, 0.146%/min, 0.068%/min (Fig.3), indicating that the Striped Field Mouse’s fur waterproofness is better than that of Grey Shrew. The experiment shows that both Striped Field Mouse and Grey Shrew have some swimming ability, but the adaptability of the Striped Field Mouse to the water environment is stronger than that of the Grey Shrew, which may be one of the reasons why it is widely distributed in the Dongting Lake area.