The invention relates to a photocuring initiation system, in particular to a free radical photopolymerization dark curing initiation system and a preparation method thereof, and belongs to the technical field of free radical polymerization preparation. The dark curing initiation system comprises the following components in percentage by weight: a first component: 0.01-1% of a photosensitizer; anda second component: 0.5-1% of a co-initiator, wherein the co-initiator is a water-soluble polypeptide having antioxidation activity and containing tyrosine residues. Compared with a previously reported dark curing photoinitiation system, the free radical photopolymerization dark curing initiation system disclosed by the invention has the advantages that the system is simple in component and is only a two-component system; the system does not contain transition metal elements, has good biocompatibility, can be used in the fields of medical health and the like, and has the advantages of easily available raw materials, good stability, long-term storage, difficulty in oxidative decomposition, low required irradiation light intensity, short irradiation time, high initiated polymerization conversion rate, less polymerization heat release amount, low polymerization system temperature, and no generation of harmful substances with strong alkalinity and strong oxidizability in the polymerizationprocess.