Abstract: We investigated the effects of a combined application of N, P and K on the yield of 8-year-old Chinese chestnut (Castanea mollissima) ‘Yanshanzaofeng’ cultivars, planted in Xiqian County of Hebei Province, over a two year period of field experiments, using a three-factor two-equation D-saturation optimal design. Based on our data obtained, the amounts of fertilization and the ratios of N, P and K were optimized with a mathematical model, in which the amounts of fertilization of N, P and K were independent variables and yield as our target variable. The results indicated that the yield was significantly affected by the application of N, P2O5 and K2O, with statistically significant interactive effects between all two factor levels. In descending order in the effect of N, P2O5 and K2O on the yield was NP2O5K2O. Results of a frequency analysis of their effect revealed that the target yield could exceed 1.62 kg per plant at a confidence interval of 95%, with the following levels of optimal fertilization: N 0.85-1.19 kg N per plant, 0.65-0.80 P2O5 kg and 0.53-0.64 K2O kg per plant. The best mass ratio of NP2O5K2O was 10.55-0.940.45-0.75. The results of the marginal yield equation showed that the yield could reach a maximum of 1.75 kg per plant with the following amounts of fertilizers: N 1.123 0, P2O5 0.754 0 and K2O 0.612 0 kg per plant and the best mass ratios of NP2O5K2O was 10.670.54.