In this study,the effects of different amount of phosphorus fertilizer（P₂O₅: 0kg/ ha,45 kg/ha,90 kg/ha and 135 kg/ha） on photosynthesis and yield of castor（Ricinus communus L.） were studied.The results showed that photosynthesis and yield of castor increased with the increase of the amount of phosphorus fertilizer.When the amount of phosphorus fertilizer was about P₂O₅ 45 kg/ha the yield of castor was highest and 32.34% higher than CK.