Swimming capacity tests were conducted on Rhynchocypris lagowskii, a typical fish species in the Songhua River Basin, to provide reference data for ecological restoration facilities. Under a water temperature of (20±1) ℃, a self-designed swimming test device was used to evaluate the swimming performance and behavior of approximately 50 individuals with body lengths of 15.75, 16.25, 16.75, 17.25, and 17.75 cm. Flow velocity was adjusted by a variable-frequency motor using an incremental velocity method.The results indicate that the induced flow velocity for R. lagowskii ranges between 0.07~0.10 m/s. The absolute critical swimming speed is determined as (0.78±0.03) m/s, with relative critical swimming speeds of 4.60~4.68 BL/s. The absolute burst swimming speed is measured as (0.95±0.06) m/s, and relative burst swimming speeds are 5.63~5.70 BL/s. Absolute critical and burst swimming speeds are found to increase with body length, while relative critical and burst swimming speeds decrease as body length increases.Three distinct swimming behaviors are observed during incremental velocity tests: upstream migration, stationary positioning against the flow, and downstream drifting. These behaviors are associated with three distinct stages of velocity progression. For fishway design targeting R. lagowskii, it is recommended that flow velocities be set to 0.47~0.62 m/s at the entrance, 0.20~0.78 m/s in resting pools, and below 0.89 m/s in vertical slots.This study supplements biological data on fish species in the Songhua River Basin and offers practical guidelines for designing fish passages and spawning habitats in ecological restoration projects.