A single crystal multi-element positive electrode material and a preparation method therefor, and a lithium ion battery. The ratio of the length of the longest diagonal line to the length of the shortest diagonal line of the single crystal particles of the single crystal multi-element positive electrode material measured by an SEM is roundness R, and R≥1; and D10, D50 and D90 of the single crystal particles of the single crystal multi-element positive electrode material satisfy: K90=(D90−D10)/D50, and the product of K90 and R is 1.20-1.40. The single crystal multi-element positive electrode material is more round and regular in morphology, the single crystal particles have uniform size, less agglomeration and less adhesion. The material has the characteristics of high compaction density, good rate capability and excellent cycle performance.