【Objective】As one of the most important food crops in China, rice (Oryza sativa L.) is the staple food for more than half of the country’s population. With the development trend of global warming and frequent occurrence of extreme weather such as sustained high temperature, drought on farmland is becoming a more frequent and urgent problem. Thus, this study seeks to clarify the effects of drought stress on rice at different growth stages, the regulation of potassium on drought stress and its mechanism, and to provide a theoretical basis for the management of potassium and efficient water use in rice.【Method】A two-factor pot experiment of K and water treatments at different periods was carried out in 2021. Potassium management was two levels of 0.15 (+K) and 0 (-K) g·kg^-1 soil (calculated as K₂O), moisture management was four levels of drought stress at the tillering stage (TD), drought stress at booting stage (BD), drought stress at milking stage (MD) and well-watered treatment (WW), to explore the effects of K fertilizer on rice yield and physiological characters under drought stress at different growth stages. 【Result】Results showed that drought stress significantly decreased rice yield. Compared with the WW treatment, TD, BD and MD treatments decreased rice yields by 53.9%, 45.2%, and 7.6% under K deficient conditions, respectively, while under K sufficient conditions, rice yields reduced by 28.3%, 16.5% and 5.9%, respectively. The degree of influence of drought stress on yield in different growth stages was: TD > BD > MD, and K deficiency aggravated the negative impact of water deficit on rice yields. Similarly, drought stress also caused a decrease in canopy transpiration rate, leaf water potential, leaf net photosynthetic rate, and limited dry matter accumulation. Compared to the WW treatment corresponding to the same period, TD and BD treatments reduced leaf biomass by an average of 42.9% and 31.2%, respectively. The stem sheath biomass decreased by 43.8% and 38.0%, respectively, and the effect of water deficiency on biomass in different growth stages was: TD > BD. Potassium deficiency resulted in a reduction in net photosynthetic rate, leaf area and chlorophyll content, which restricted the ability of plants to receive light radiation and produce dry matter. Compared with the K-sufficient treatment, the leaf biomass of the TD and BD and WW treatments at the same stages decreased by 52.6%, 32.7%, 42.1%, and 31.2%, respectively. Also, under potassium deficient conditions, stem sheath biomass decreased by 55.3%, 63.6%, 52.2%, and 28.0%, respectively. Drought stress exacerbated the negative effects of potassium deficiency. 【Conclusion】Our results indicated that drought stress could limit the net photosynthetic rate and leaf water potential, resulting in the reduction of rice yield, which affects the tillering stage and booting stage more than the milking stage. Potash application significantly increased leaf area, increased chlorophyll content, enhanced the ability of rice to intercept light radiation, improved rice photosynthetic efficiency, and increased rice dry matter accumulation, while reducing canopy transpiration rate, improving water use efficiency, alleviating the decline of leaf water potential, thereby enhancing the drought resistance of crops.