The invention relates to a method for reducing the levels of crude protein and phosphorus in a fattening pig compound feed. According to the method, monomer lysine, methionine and phytase are added into the pig compound feed, wherein every 1 kilogram of premix monomer comprises 100-150g of lysine, 60-100g of methionine, 2.50g of copper, 8.00g of zinc, 8.00g of iron, 4.00g of manganese, 15mg of iodine, 20mg of selenium, 50g of compound multi-vitamin for pigs and 10-20g of phytase. According to the method, the defect caused by the fact that the absorption of the mineral elements is influenced because pigs do not have enzyme for digesting the phytate phosphorus and phytate phosphorus is chelated with other divalent and trivalent metal elements such as calcium, magnesium, zinc and iron to form compounds which are very difficult to dissolve is overcome; and the method has the effect of reducing the levels of nitrogen and phosphorus in the fattening pig compound feed at the same time without reducing the production property of the pigs and has the advantages of satisfying the nutritional requirements of the pigs, saving the bean pulp without influencing the production property of the pigs, and discharging nitrogen.