In order to reveal the law of soil erosion of different canopy density Pinus massoniana forests in the red soil erosion area of southern China, the standard runoff plot observation method was adopted in different canopy density (0.2, 0.4, 0.6, and 0.8) Pinus massoniana forest in the Changting of Fujian Province. A rainfall gradient was constructed to analyze the variation of soil erosion with the rainfall level of different canopy density Pinus massoniana forests based on the 37 natural rainfall events observed in 2015. The correlation between runoff and sediment yield and rainfall factors was conducted. The results showed that:(1) The runoff and sediment yield of different canopy density Pinus massoniana forests increased gradually with the increase of rainfall grade, and the increase was more obvious under rainstorm condition. (2) Under three rainfall grades such as moderate rain, heavy rain, and rainstorm, the runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.2 and 0.8 were higher than that with the canopy density of 0.4 and 0.6. The runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.4 and 0.6 showed less variation with the increase of rainfall grades. (3) The runoff and sediment yield of different canopy density Pinus massoniana forests were significantly correlated with rainfall and rainfall erosivity (P<0.05) under the natural rainfall gradient. (4) The stepwise regression analysis showed that the main variables of the regression equation of the runoff of Pinus massoniana forests with different canopy density are rainfall and the maximum 30 min rain intensity, while of the sediment yield regression equation are rainfall and rainfall erosivity. In summary, the higher or lower degree of canopy pine forest is not conducive to soil and water conservation, and the most effective canopy closure degree of Changting red soil erosion is 0.6 to control the soil and water erosion of Pinus massoniana forests.