The invention provides a thioxanthone visible light initiator, a preparation method and an application. The structure of this thioxanthone visible photoinitiator is shown in formula (I), wherein R is benzyl, 4-dimethylaminobenzyl, 4-methylbenzyl, 3-methylbenzyl, 2-methyl Benzyl, 4-benzyloxybenzyl, 4-methoxybenzyl, 3-(trifluoromethyl)benzyl, 4-bromobenzyl, 3-cyanobenzyl, 3-nitrobenzyl, 2-(trifluoromethyl)benzyl, 3,5-bis(trifluoromethyl)benzyl or 4-cyanobenzyl. The thioxanthone visible light initiator provided by the present invention has good compatibility with acrylates, can effectively initiate monomer polymerization without additives, and can initiate epoxy and ethylene polymerization when used in combination with iodonium salts. Cationic polymerization or radical-cationic polymerization of base ether monomers has high initiating activity and simple structure, which is beneficial to industrial production.