Low soil phosphorus (P) availability and drought are the most recognized growth-limiting factors for the cotton production in arid regions. A pot experiment with P-efficient (Xinluzao19, X19) and P-inefficient (Xinluzao19, X26) cotton cultivars was conducted to investigate the effects of P and drought on dry matter accumulation and P efficiency. Results showed that biomass and chlorophyll content of leaves increased significantly with the increase in soil P content, whereas the root:shoot ratio decreased dramatically. Drought increased the root:shoot ratio, but the chlorophyll content of leaves remained stable. The yield of X19 increased with the increase in soil P content. For X26, the highest yield was attained under the medium P content. Under drought conditions, root P efficiency ratio, P absorption efficiency, and P transfer efficiency were all proportional to P concentration, whereas P utilization was inversely proportional. Compared with X26, X19 presented higher P absorption efficiency and P utilization but lower root P efficiency ratio and P transfer efficiency. It suggested thatthe application of phosphate fertilizer under drought could increase the root P efficiency ratio, P absorption efficiency, and P transfer efficiency, thereby enhancing the ability of stress resistance of cotton and significantly increasing biomass as well as cotton yield.