Abstract: Mastering the impact of converting Pinus massoniana forest to Torreya grandis forest on the surface runoff and the nitrogen and phosphorus loss could provide a certain foundation for the artificial forest management. Three types of runoff treatment plots, namely Pinus massoniana forest, young Torreya grandis forest, and middle-aged Torreya grandis forest, were set up at the Forestry General Farm in Dongyang City, Zhejiang Province. The surface runoff in 2023 was comprehensively monitored, and the concentrations of different forms of nitrogen and phosphorus in the runoff were analyzed, and the nutrient loss was calculated. The results showed that the amount of surface runoff was as follows: Pinus massoniana forest (218.0 m³·hm⁻²)＞young Torreya grandis forest (206.0 m³·hm⁻²)＞middle-aged Torreya grandis forest (157.0 m³·hm⁻²). The amount of surface nitrogen loss was as follows: young Torreya grandis forest (806.56 g·hm⁻²)＞middle-aged Torreya grandis forest (582.80 g·hm⁻²)＞Pinus massoniana (159.89 g·hm⁻²), while the amount of phosphorus loss was as follows: young Torreya grandis forest (265.55 g·hm⁻²)＞middle-aged Torreya grandis forest (183.57 g·hm⁻²)＞Pinus massoniana forest (48.72 g·hm⁻²). Compared with the Pinus massoniana forest, the surface runoff of young and middle-aged Torreya grandis forests decreased by 5.5% and 22.5%, respectively, while the nitrogen loss increased by 4.04 and 2.65 times, and phosphorus loss increased by 4.45 and 2.77 times. In summary, the transformation of Pinus massoniana forest into Torreya grandis forest reduced the surface runoff, but increased the loss of nitrogen and phosphorus. As the age of Torreya grandis forest increased, the amount of surface runoff and nitrogen and phosphorus loss decreased.