Abstract: In the northwestern arid areas with severe shortage of water resources, the comprehensive use of recycled water is one of the important means to effectively alleviate the shortage of water resources. For Yinchuan City, which is relatively rich in lake wetland resources, it is of great significance to carry out ecological rehydration of natural rivers and lakes, but the ecological risks of recycled water used for ecological rehydration of rivers and lakes cannot be ignored. Taking Yuehai Lake, a typical lake in Yinchuan City, as the research object, through indoor simulation experiments, the effects of different proportions of recycled water replenishment on water quality and microorganisms of Yuehai Lake were studied. The research results showed that with the increase of the proportion of recycled water replenishment, the concentrations of total nitrogen, nitrate nitrogen and total phosphorus increased significantly, but gradually decreased in the later stage of the experiment. Dissolved oxygen as a whole showed a downward trend, while the chemical oxygen demand showed the characteristics of first decrease, then rise and then decrease. The turbidity first decreased and then increased, and pH gradually stabilized after a sharp rise in the middle of the experiment, and the electrical conductivity was on the rise and there was a stratification phenomenon. Amorphous phylar was the dominant phylar, and its proportion increased significantly with the increase of the proportion of rehydration and the hydration time. The proportion of mycobacterium phyllus and the wart microphyll gradually decreased. When the ratio of recycled water replenishment was 50%-60%, although the concentration of total nitrogen and total phosphorus increased in the early stage, it decreased rapidly in the later stage under the action of microbial assimilation and self-cleaning. The dissolved oxygen stabilized above 6 mg/L, and the turbidity and chemical oxygen demand changed the least. At the same time, the richness and diversity of microbial species under this ratio were high, the proportion of metamorphic phylar was maintained at about 85%, and the community structure was rich and stable. Redundancy analysis showed that nitrate nitrogen, pH and total phosphorus had a significant impact on the microbial community structure, but the three fluctuations were the weakest and the ecological position was the most stable in the 50%-60% groups. Comprehensive water quality safety and biodiversity, the ratio of 50% to 60% recycled water replenishment is the optimal range for the ecological replenishment of Yuehai Lake, which can realize the efficient recycling of water resources while ensuring the landscape function.