The experiment results showed that pH of the red earth in hilly orangery was decreased with increasing amount of N applied (r=-0.905) on the basis of the application of organic manure, P and K fertilizers. The mandarin yields varied greatly with the amounts of N applied (y=33.02+12.94x+5.07x²-6.04x³).After application of N the mandarin yield had a significant or correlation with the contents of available N, P and K in the soil and leaves. The invert sugar, reducing sugar and V. C contents were linearly correlated with the amount of N applied but the total acidity was negatively correlated with the of N applied (r=-0.918).So N application could raise the quality of mandarin.