Abstract: In order to study the influence of internal structure in culvert fish-way on hydraulic characteristics and fish passage performance, a culvert evaluation software named Fish Xing was applied to predict and evaluate the existing passage barriers of the culvert crossing the Nanchang high way, an optimized hydraulic solution was presented as well, which was aimed at the results of barrier evaluation for internal structure in culvert. The data of flow field monitored in the retrofitted culvert fish-way confirms that the watervelocity in each pool increases by about 30% compared to that of the smooth culvert with no baffle system, while the water level difference between adjacent pool declines after the construction of high-and-low weir baffle system. According to the results of fish passage efficiency using RFID (Radio Frequency Identification) technology under different flow discharges, it can be seen that the rate of successful passage for grass carp (Ctenopharyngodon) significantly exceeds that of native crucian carp (Carassius auratus) and carp (Cyprinus carpio), the corresponding rates are 50%, 26.41% and 7.6% respectively. As the water flow rate in culvert increases from 0.378 m³/s to 0.429 m³/s, both the average time and shortest time for grass carp to pass through the upstream entrance of culvert decline to a certain extent, while the average time consumed by native carp in passing through the whole culvert extends by 35.15%, and the rates of retracing back increase slightly for both grass carp and crucian carp.