Dam construction alters natural river flows and hydrological regimes, including water temperature regimes, and this is a key environmental factor influencing fish reproduction. The aim of this study was to investigate the distribution and replenishment mechanism of the early population of silver cap, Hypophthalmichthys molitrix under the influence of the cascade hydropower station on Jinsha River Dam. Based on the early resource survey data of three sections [Yibin (YB), Luzhou (LZ) and Jiangjin (JJ)] in the upper Yangtze River reaches taken from May to July of 2017 to 2019, generalized additive models with Tweedie distribution were used to analyze the major environmental factors influencing their temporal and spatial patterns. The results revealed that the density of silver carp eggs showed a consistent trend from 2017 to 2019. Spatially, no H. molitrix egg was collected at YB, which was closest to the dam in the three river sections, whereas the density of H. molitrix eggs was highest at JJ, which was the farthest from the dam with the highest flow and water temperature and the lowest water transparency. Temporally, the density of fish eggs in June was significantly higher than that in May and July, suggesting that June was the peak breeding period of H. molitrix in the upper reaches of the Yangtze River. Generalized additive model analysis indicated that water discharge, distance from the dam, water transparency, and water temperature were the main environmental factors significantly affecting the spatial distribution of fish egg density with different relative contributions, together explaining more than 48.9% of total deviance observed (P＜0.05). The highest interpretation rate of the deviation of the flow was 29.4%, followed by 8.7% by the distance from the dam. Density distribution of H. molitrix egg were mainly in the range of water temperature 21–23 ℃, flow rate 6000‒14000 m³ /s, and transparency of less than 50 cm. Comprehensive analysis indicates that the low-temperature, low-flow, and high-transparency water released by the dam operation impact the natural reproduction of H. molitrix in the river section near the dam, while the degree of dam impact on fish reproduction is gradually weakened by increasing distance on the dam and the inflow of tributaries along the river, thus forming the longitudinal recovery gradients. The correlation analysis between spawning yield and hydrological indexes showed that the quantity of fish eggs was positively correlated with the duration of water rise and the increase of discharge (P＜0.05). The natural reproduction of H. molitrix in the upper reaches of the Yangtze River benefits when the duration of water rise lasts for more than four days and the cumulative increase of flow exceeds 5030 m³ /s. Additionally, the spawning activities of H. molitrix showed a tendency to migrate upstream in the post-dam of the Three Gorges Dam, and the upper reaches of the Yangtze River from Baisha Town to Rongshan Town were the main spawning grounds of H. molitrix. Hence, the river sections further away from the dam, especially the Chongqing-Luzhou section above the reservoir tail, are suggested to be protected as the key breeding area for the growth and sustenance of H. molitrix population.