The photo-induced electron transfer has been investigated for the process of photo-initiation polymerization. Both photo-initiated free radical formation and photo-acid generation processes are discussed. The phenomenon of fluorescence quenching is used as an important criterion for confirming the electron transfer process occurred. The competitions of the decay process of excited species between electron transfer and energy transfer or between intra-molecular charge transfer and inter-molecular electron transfer determine the direction of reaction concerned. The design and the synthesis of new compounds used as photo-initiators or photo-sensitizers become a key problem for the developing of this field.