The invention belongs to the field of organic synthetic chemistry, and in particular relates to a preparation method of dimethyl sulfone as well as used catalyst and catalyst composition thereof. The general formula of the catalyst is aFe2O3.bMnO2.cTiO2.dRh203.eRuO2, wherein a, b and c are selected from 0 to 15 independently, and d and e are selected from 0.01 to 10 independently. The catalyst composition comprises the catalyst and photosensitizer with the mass ratio of 1:0.01 to 10. The catalyst/catalyst composition has efficient catalytic activity, oxygen is taken as single oxidant during a process of catalyzing dimethylsulfide or dimethyl sulfoxide to prepare dimethyl sulfone, and compared with a conventional nitric acid technique and a potassium permanganate method, the preparation method has the advantages that during preparation, any hazardous substances can not be caused, and pollution is not caused to the environment.