A preparation method of a composite positive electrode material, comprising the following steps: providing a kernel material, wherein the kernel material contains a lithium-rich metal oxide, and a surface of the lithium-rich metal oxide comprises a free lithium compound; providing a positive electrode active material precursor; attaching the positive electrode active material precursor to at least a partial surface of the kernel material; and making the positive electrode active material precursor react with the free lithium compound comprising: performing heat treatment at 600°C-800°C in a protective gas atmosphere for 2 hours to 8 hours; so that a positive electrode active material is formed on at least a partial surface of the lithium-rich metal oxide, to obtain the composite positive electrode material; wherein the free lithium compound comprises one or more of Li 2 O, LiOH, and Li 2 CO 3, and a mass percentage of the free lithium compound in the kernel material that is obtained through titration is 0.5wt%-15wt%; wherein the titration measurement is defined in the description; wherein the lithium-rich metal oxide is selected from one or more of Li 2 M 1 O 2, Li 2 M 2 O 3, Li 3 M 3 O 4, Li 5 M 4 O 4, and Li 6 M 5 O 4, wherein M 1 comprises one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, and Cu; M 2 comprises one or more of Mn, Sn, Mo, Ru, and Ir; M 3 comprises one or more of V, Nb, Cr, and Mo; M 4 comprises one or more of Fe, Cr, V, and Mo; M 5 comprises one or more of Co, V, Cr, and Mo; and a valence state of each metal element other than Li in the lithium-rich metal oxide is lower than a highest oxidation valence state of the metal element; and wherein the positive electrode active material precursor is selected from one or more of Ni x1 Co y1 Mn z1 2, Ni x2 Co y2 Al z2 2, Ni x3 Co y3 Mn z3 CO 3, Ni x4 Co y4 Al z4 CO 3, and MPO 4, and further optionally selected from one or more of Ni x1 Co y1 Mn z1 2, Ni x2 Co y2 Al z2 2, and MPO 4, wherein x1+y1+z1=1, x2+y2+z2=1, x3+y3+z3=1, x4+y4+z4=1, and M is selected from one or more of Fe, Ni, Co, and Mn. providing a kernel material, wherein the kernel material contains a lithium-rich metal oxide, and a surface of the lithium-rich metal oxide comprises a free lithium compound; providing a positive electrode active material precursor; attaching the positive electrode active material precursor to at least a partial surface of the kernel material; and making the positive electrode active material precursor react with the free lithium compound comprising: performing heat treatment at 600°C-800°C in a protective gas atmosphere for 2 hours to 8 hours; so that a positive electrode active material is formed on at least a partial surface of the lithium-rich metal oxide, to obtain the composite positive electrode material; wherein the free lithium compound comprises one or more of Li 2 O, LiOH, and Li 2 CO 3, and a mass percentage of the free lithium compound in the kernel material that is obtained through titration is 0.5wt%-15wt%; wherein the titration measurement is defined in the description; wherein the lithium-rich metal oxide is selected from one or more of Li 2 M 1 O 2, Li 2 M 2 O 3, Li 3 M 3 O 4, Li 5 M 4 O 4, and Li 6 M 5 O 4, wherein M 1 comprises one or more of Ni, Co, Fe, Mn, Zn, Mg, Ca, and Cu; M 2 comprises one or more of Mn, Sn, Mo, Ru, and Ir; M 3 comprises one or more of V, Nb, Cr, and Mo; M 4 comprises one or more of Fe, Cr, V, and Mo; M 5 comprises one or more of Co, V, Cr, and Mo; and a valence state of each metal element other than Li in the lithium-rich metal oxide is lower than a highest oxidation valence state of the metal element; and wherein the positive electrode active material precursor is selected from one or more of Ni x1 Co y1 Mn z1 2, Ni x2 Co y2 Al z2 2, Ni x3 Co y3 Mn z3 CO 3, Ni x4 Co y4 Al z4 CO 3, and MPO 4, and further optionally selected from one or more of Ni x1 Co y1 Mn z1 2, Ni x2 Co y2 Al z2 2, and MPO 4, wherein x1+y1+z1=1, x2+y2+z2=1, x3+y3+z3=1, x4+y4+z4=1, and M is selected from one or more of Fe, Ni, Co, and Mn.