3 kinds of melamine formaldehyde (MF) resin synthesized in laboratary and separated naturally in both aqueous and precipitate phases during storage were analyzed by C13 NMR,aiming at understanding effect of different structural groups of MF resin and caprolactam on storage stability.Results showed that storage life of the MF resins could be changed with substitute degree of amine group of melamine.The MF resins with structure such as NH—CH2—OCH2OH and NH—CH2OCH2—NH would be more stable in aqueous phase than NH—CH2—NH.The dissolubility of the MF resins with structure such as NH—CH2—NH in aqueous phase was improved due to additional caprolactam.But it is not sure that cocondensation of caprolactam with the MF resins was occurred during synthesizing.