The invention relates to a preparation method of di (2,4,6-trimethylbenzoyl) phenyl phosphine oxide and (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide used in the technical field of radiation polymerization curing new materials, hydrogen phosphide as a raw material is reacted with chlorobenzene or bromobenzene and 2,4,6-trimethylbenzoyl chloride, and an acyl oxygen phosphonic compound is obtained by oxidizing with an oxidant. By adjusting the feed ratio, the di (2,4,6-trimethylbenzoyl) phenyl phosphine oxide and the (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide are respectively obtained, and the purpose for simultaneously producing the two target products of di (2,4,6-trimethylbenzoyl) phenyl phosphine oxide and the (2,4,6-trimethylbenzoyl) diphenyl phosphine oxide can be achieved by use of same material and device, and compared with known technology paths reported in literatures, the preparation method has the significant advantages of novelty of the chemical reaction technology, cost economic competitiveness and environmental friendliness.