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[Objective] The present paper aimed to investigate the mechanism of yield and carbon assimilates metabolism in cotton varieties of different genotypes in response to low phosphorus stress, and to provide a theoretical basis for the physiological regulation of cotton yield and quality under low phosphorus stress in production. (Method) In the study, a pot experiment was conducted with low phosphorus tolerant genotypes (BX014 and LuYuan343) and low phosphorus sensitive genotypes (FJA and DLNTDH), and low phosphorus (P1, 15 mg/kg), medium phosphorus (P2, 50 mg/kg), normal phosphorus (P3, 150 mg/kg), and high phosphorus (P4, 300 mg/kg) were used as the experimental materials. Four treatments were used to study the effects of different phosphorus application levels on dry weight, phosphorus uptake and utilization, yield traits, and carbohydrate metabolism of cotton bolls and their correlation between carbon assimilates metabolizing enzyme activities and yield. [Result] (i) Under low phosphorus stress, the dry weight accumulation of different organs, phosphorus accumulation, plant height, number of fruiting branches, number of fruiting nodes, number of bolls, weight of bolls, seed cotton yield, lint yield and clothing fraction of cotton would be significantly reduced, while the phosphorus utilization efficiency and boll abscission rate would be significantly increased, and there was a significant reciprocal effect between different phosphorus treatments and varieties. (ii) Carbohydrate content in boll-opposed leaves was the key substance in response to low phosphorus stress; Under low phosphorus treatment, with the increase of phosphorus content, cotton boll-opposed leaves sucrose and soluble sugar content generally showed a decreasing trend, and the activities of phospho-sucrose synthetase (SPS) and sucrose synthetase (SuSy) showed a tendency to increase firstly and then decrease. (iii) Under P1, P2 and P4 treatments, the cotton dry weight, phosphorus accumulation, phosphorus utilization efficiency and yield indexes of the low phosphorus tolerant genotypes were significantly higher than those of the low phosphorus sensitive genotypes, and the response to low phosphorus stress was not uniform, showing strong low phosphorus tolerance; And the activities of SPS and SuSy were significantly higher than those of the low phosphorus sensitive genotypes, and the difference in the enzyme activities might be one of the reasons for the low phosphorus tolerance of low phosphorus tolerant genotypes. The differences in enzyme activities may be one of the reasons for low phosphorus tolerance in low phosphorus tolerant genotypes. (iv) The correlation analysis of the traits showed that lint yield was extremely significant positive correlated with boll weight (correlation coefficient was 0.95), SPS (correlation coefficient was 0.96) and SuSy activity (correlation coefficient was 0.99), respectively. [Conclusion] Higher SPS and SuSy activities in the opposite leaves of cotton bolls of low phosphorus tolerant genotypes under low phosphorus stress maintain the ability of sucrose synthesis, which in turn promotes the redistribution of sugar, thus ensuring the production and accumulation of dry matter under low phosphorus conditions and thus increasing lint yield. [ABSTRACT FROM AUTHOR]