Abstract: To assess the variation of fish resources caused by cascade development, we used a split-beam echosounder (120 kHz, 250 W) with catch statistics and a geographic analysis to investigate the spatiotemporal variation and to estimate the existing resource abundance in Yantan Reservoir in the Red River in September, 2015. The average fish resources density was (0.53±2.11) ind·m^-2 with an increasing trend from upper to the Reservoir. The density distribution of fish resources had no significant correlation with water depth. The fish mainly distributed at 0~20 m layer. For water depth, individuals at different sizes had definite selectivity (86.2%):small fish ( < 10 cm) distributed within the 30 m layer and about 44.7% large fish (>30 cm) distributed at water layer deeper than 40 m. Based on the GIS fish distribution model, the fish resources abundance was about 6.57×10⁷individuals.