The performance and behavior of epoxy latex coatings are different from solvent-type ones.It is decided by the distinct curing mechanism. The solvent-type epoxy film obtained from epoxy resin and curing agent by homogeneous reaction, namely, the state of epoxy resin and curing agent is uniform. However, epoxy latex film made from epoxy resin emulsion or dispersion and water soluble amine by polyphase reaction. So the determination of potlife of epoxy latex can be showed by film gloss changes with residence time, dissimilar with solvent-type by the index of viscosity. The modern infrared spectrum measure shows that the epoxy groups in the dried epoxy latex film exist even if EEW to HAV proportion is 1.2:1. This also testifies the incomplete polyphase reaction mechanism of epoxy emulsion coating curing at ambient temperature.