【Objective】This paper is oriented to study rational application of pig manure and its effect on soil fertility in upland red soil.【Method】A 3-year stationary field experiment on application of pig manure was carried out for the study. The experiment was designed to have 5 different application rates for pig manure, that is, 0, 7.5, 15, 30 and 45 t∙hm^-2. Samples of the soils and the crops, i.e. spinach and maize were collected from the plots with different manure application rate for analysis biomass of the shoots, relevant soil physico-chemical properties, and activity of the enzymes involved in C, N and P recycling with the microplate flurimetric assay method. 【Result】Results shown that soil organic matter, total N, P and K, readily available P and K and biomass of spinach and maize shoots all increased linearly with increasing pig manure application rate. In the plot applied with 45 t∙hm^-2 of pig manure, the highest average biomass of shoots reached 11.48 and 20.84 t∙hm^-2 in spinach and maize, respectively, organic matter, total nitrogen, total phosphorus rise up to 14.6, 1.07 and 0.73 g∙kg^-1 and available nitrogen, alkalyzable phosphorus and readily available potassium did up to 85.47, 106.9 and 411.7 mg∙kg^-1, respectively; But there was no significant differences in soil nutrient elements contents between 15, 30 t∙hm^-2 of pig manure treatments and 45 t∙hm^-2 of pig manure treatment. Moreover, activities of the 6 kinds of soil enzymes involved in C, N and P cycling (β-1,4-Glucosidase, βG; β-1,4-Xylosidase, βX; Cellobiohydrolase, CBH; Leucine amino peptidase, LAP; β-1,4-N-Acetyl-glucosaminidase, NAG; Acid phosphatase, AP) were linearly related with pig manure application rate, especially in the plots applied with 30 or 45 t∙hm^-2 and remarkablely or extreamly remarkablely and positively related to contents of soil organic matter and soil nutrients. In the plot applied with 45 t∙hm^-2 of pig manure, βG, βX, CBH, LAP, NAG and AP enzymes reached up to 105.3, 17.49, 36.63, 47.76, 55.31 and 77.38 nmol∙g^-1∙h^-1, respectively. C/N did not much in plots applied with different rates of pig manure, βG/(NAG+LAP) decreased with increasing application rate of pig manure, while (NAG+LAP)/AP exhibited a reverse trend. 【Conclusion】Soil organic matter, nutrient content and enzyme activity of the soil increase with application rate of pig manure in the red upland soil, and crop yield does linearly. Attention must be paid to problems, such as increased nitrogen and phosphorus loss, as a result of excessive available nutrients in the soil.