This application discloses a positive electrode active material and a preparation method thereof, a positive electrode plate, a lithium-ion secondary battery, and a battery module, battery pack and apparatus related thereto. The positive electrode active material includes secondary particles formed by agglomeration of primary particles, where the primary particles are a lithium transition metal oxide, and a transition metal site of the lithium transition metal oxide includes nickel and a doping element; and a Young's modulus E of the primary particles satisfies 175 GPa≤E≤220 GPa.