Abstract: The Yangtze finless porpoise (Neophocaena asiaorientalis, YFP) is mainly distributed in Poyang Lake, Dongting Lake, and the middle and lower reaches of the Yangtze River and its tributaries in China. The heavy vessel traffic in these areas inevitably impacts YFPs. Our research group conducted a 112-day vessel-based survey on YFPs in Nanjing from 2019 to 2023 using the line transect sampling method to study the impacts of vessels on porpoise behavior. The results showed that the presence of ships changed the behavior of the YFPs, with the proportion of foraging behavior decreasing from 48% to 33%, while travel behavior increased from 32% to 43%. The distance of vessels from the YFPs had significant impacts. When vessels were over 300 meters away, YFPs showed a 95% neutral response, with no observed escape behavior. However, within 300 m, the frequency of escape reactions increased, reaching nearly 30% within 100 m. The vessel type and cluster size had slight, non-significant impacts on YFP behavior. In conclusion, the presence and proximity of vessels significantly impact the normal activities of YFPs. Therefore, strict restrictions on navigation routes are necessary to prevent vessels from traveling nearshore areas where porpoises are concentrated, in order to maximize the protection efficiency for this species.