Abstract: Temporal and spatial variations of sexual reproduction in a remnant population of the endangered species Myricaria laxiflora (Franch.) P. Y. Zhang et Y. J. Zhang were investigated based on changes in flowering and fruiting traits with elevation on Guanzhou Island, Zhijiang, China. The impact of cascade water conservancy and hydropower construction projects on the sexual reproduction of remnant populations was analyzed based on the characteristics of water-level fluctuations in the habitat of M. laxiflora. Results showed significant differences in the sexual reproduction of the remnant population at different elevations. Flower branch number per plant, flower number per branch, and flower number per plant of plants at the upper part of the fluctuation zone were 66.09%, 50.14%, and 98.63% higher than those at the middle part, and 79.50%, 283.33%, and 461.05% higher than those at the lower part, respectively. Fruit branch number per plant, fruit number per branch, fruit number per plant, seed number per fruit, and seed germination percentage of plants at the upper part of the fluctuation zone were 60.17%, 25.26%, 88.05%, 6.96%, and 30.69% higher than those at the middle part, and 97.39%, 82.45%, 208.31%, 19.12%, and 45.91% higher than those at the lower part. Correlation analysis showed significant correlations between the flowering and fruiting characteristics and elevation, plant exposure period, soil water content, and temperature. The influence of environmental factors on sexual reproduction was in the order of exposure time, elevation, daily average temperature, and soil moisture content.