The present invention provides a method for preparing a positive active material for a secondary lithium battery. The method includes the steps of: synthesizing an intermediate product of a core represented by formula LixMyN1-yO2-αAβ; adding P source into the intermediate product to obtain a phosphate which does not contain lithium; and adding lithium source into the mixture of the phosphate and LixMyN1-yO2-αAβ and sintering to obtain the positive active material for secondary lithium battery. The method for preparing a positive active material for a secondary lithium battery of the present invention has the following advantages: 1) the P source can be dispersed on the surface of the core more uniformly; 2) the coating layer can be bonded to the core more tightly; and 3) the positive active material has higher rate discharge performance.