The invention discloses a method for preparing feed grade calcium phosphate with effects of reducing magnesium and supplementing calcium. The method for preparing the feed grade calcium phosphate with the effects of reducing magnesium and supplementing calcium comprises the following steps: adding a reaction promoter-calcium nitrate in a certain rate in neutralization reaction, and thus the aim of increasing the content of calcium of a product, wherein the ratio of the added amount of the reaction promoter to the molar content of magnesium in filtrate obtained after defluorination is carried out for a period of time is 0.2-2.0, the reaction promoter is added when the pH value is 4.0-5.0 during the neutralization reaction, and the reaction temperature is controlled to be 20-50 DEG C. The method for preparing the feed grade calcium phosphate with the effects of reducing magnesium and supplementing calcium has the advantages that precipitation of magnesium ions is effectively inhibited, after the reaction is finished, the magnesium ions are almost left in a liquid phase, and the aim of increasing the content of calcium in the feed grade calcium phosphate product is achieved.