To quantitatively assess the fish-passing efficiency in the Laluo Fishway and identify its optimal environmental conditions, on-site observations of the flow field, water temperature, and number of passing fishes were conducted in the Laluo Fishway. A two-dimensional mathematical model of the Laluo Fishway was constructed and verified to obtain more detailed flow field data, and the diurnal and seasonal rhythms of fish-passing were analyzed. The results indicate that the Laluo Fishway experienced a fish-passing peak in April, May and July. Flow velocity is the key factor influencing fish-passing efficiency. The average flow velocity at the vertical slot between 74.8% and 81.2% of the target species wuimming speed is the most favorable condition for their upstrean migration. Water temperature is also identified as a significant factor, positively correlated with the upstream migration behavior of fishes. Futhermore, a significant threshold effect is observed with a recommendation to maintain water temperatures above 8℃. Additionally, Flow has a relatively small impact on fish behavior. A flow rate in the range of 0.4-0.8 m³/s is determined to be most favorable for fish-passing.