Positive electrode material and preparation method thereof, positive plate and secondary battery

The invention provides a positive electrode material and a preparation method thereof, a positive plate and a secondary battery. The positive electrode material comprises first lithium cobalt oxide particles, second lithium cobalt oxide particles and third lithium cobalt oxide particles, wherein the particle size R1 of the first lithium cobalt oxide particles Dv50, the particle size R2 of the second lithium cobalt oxide particles Dv50 and the particle size R3 of the third lithium cobalt oxide particles Dv50 meet the relation that R3 > R2 > R1; the masses m1, m2 and m3 of the three lithium cobalt oxide particles meet the relation that m3/(m1 + m2) is greater than or equal to 0.1% and less than or equal to 1.1%. Compared with the prior art, the positive electrode material provided by the invention has the advantages that the particle size of the third lithium cobalt oxide particles is larger than the particle size of the first lithium cobalt oxide particles and the second lithium cobalt oxide particles, and the