The effect of P2O5 on the quality of tobacco leaves was studied through the experiment of different amounts of calcium magnesium phosphate fertilizer. The experiment adopted a randomized block design, four treatments were repeated three times, and 12 plots were applied with calcium magnesium phosphate fertilizer 15 kg (T2), 30 kg (T3), 45 kg (T4) and blank control (T1). The results showed that when tobacco was planted on the yellow mud soil in Hengyang County, the P2O5 application rate was suggested to be between 8.1~8.9 kg/mu, which could not only promote the vigorous growth of tobacco (plant height, stem circumference, pitch, leaf area and effective leaf number were the best), but also increase the yield, increase the proportion of medium and top grade tobacco, improve the quality and increase the income of farmers.