The fluorescence characteristic of various free radical photoinitiators was investigated by fluorescence spectroscopy. The influence of conjugated structure on fluorescence spectrum was analyzed from the molecular structure. The results show that: the wave length of fluorescence excitation spectrum gradually augments with the conjugative effect enhancement, and so does the peak of fluorescence emission spectrum. The transient fluorescence spectrum of photoinitiator is affected by electron groups and the fluorescence decay of photoinitiators with electron-withdrawing groups is faster than that of photoinitiators with electron-donating groups. The excitation peak of photoinitiator has evident red shift with the polarity of solvent increasing, which shows that transition type is π—π* transition, and the fluorescence decay is postponed with the solvent glutinosity changing. When the photoinitiator density is at 10-2mol·L-1, the fluorescence decay is evidently fast because of quenching effect caused by self-absorption and collisions between particles.