Provided are a positive electrode active material with a core-shell structure, a preparation method of positive electrode active material, a positive electrode plate, a secondary battery, a battery module, a battery pack, and an electric apparatus. The positive electrode active material includes a core containing LimAxMn1-yByP1-zCzO4-nDn, a first coating layer covering the core and containing a crystalline pyrophosphate MaP2O7 and an oxide M′bOc, and a second coating layer covering the first coating layer. The positive electrode active material in this application can reduce the generation of Li/Mn antisite defects, reduce the dissolution of manganese, and decrease the lattice change rate, increasing the capacity of the secondary battery and improving the cycling performance, high-temperature storage performance, and safety performance of the secondary battery.