In view of the serious shortage of soil and water resources in mountain orchards on the Loess Plateau, and the serious ineffective evaporation of soil, the quality and high yield of fruit trees are severely restricted. In this study, 8 years old apple (Malus pumila Mill.) was selected as the object, and the irrigation level [the upper and lower limits of soil moisture were controlled by the percentage of soil moisture content to field water capacity θf. W1 (85%~ 95%θf), W2 (75%~85%θf), W3 (65%~75%θf) and W4 (55%~65%θf)] and nitrogen application levels [N1 (600 kg·ha− 1), N2 (450 kg·ha− 1), N3 (300 kg·ha− 1), N4 (150 kg·ha− 1)], the effects of water and nitrogen regulation on yield, water and nitrogen use efficiency and quality of apple were analyzed, and the indexes of apple were evaluated by multi-objective comprehensive evaluation. The results showed as follows: (1) Apple yield first increased and then decreased with the increase of irrigation amount and nitrogen application amount, and there was an obvious threshold value. The irrigation amount and nitrogen application amount corresponding to the highest apple yield (36637.09 kg·ha− 1) in 2020 were 93.89 mm and 501.73 kg·ha− 1, respectively. The irrigation amount and nitrogen application amount corresponding to the highest apple yield (38419.43 kg·ha− 1) in 2021 were 93.09 mm and 498.51 kg·ha− 1, respectively. Water and nitrogen regulation significantly affected the water and nitrogen use efficiency of apples. The water use efficiency and partial factor productivity of nitrogen of the treatment with moderate irrigation amount and nitrogen application amount (W2N2) were significantly higher than those of the other treatments. Suitable water and nitrogen supply could improve the quality indexes of soluble solid, vitamin C and soluble sugar of apples, reduce the hardness and fruit shape index, and significantly improve the fruit quality. (2) The evaluation ranking of comprehensive production effect of apples under different treatments was significantly inconsistent due to different evaluation methods. Fuzzy Borda method was used to combine the results of principal component analysis method, membership function method, rank sum ratio method and entropy weight TOPSIS method, and it was concluded that W2N1 treatment ranked the highest in terms of evaluation value in 2020 and 2021, that is, the comprehensive effect of this treatment was the best. (3) Based on the fuzzy Borda combination evaluation method, the comprehensive effect evaluation value of apples was evaluated by regression analysis. When the water and nitrogen supply thresholds in 2020 and 2021 are 92.18 ~ 97.03 mm, 519.83 ~ 547.19 kg·ha− 1 and 90.32 ~ 95.07 mm, 461.57 ~ 485.86 kg·ha− 1, The comprehensive production effect of apples is better, and it is a water and nitrogen supply model for improving apple quality and increasing efficiency on the Loess Plateau.
