A copolymer containing hydrophobic monomers(styrene, methyl methacrylate and butyl acrylate)and hydrophilic momomer (acrylacrylic acid)was synthesized by solution polymerization, and then neutralized by N,N-diethylamino ethanol to form soap-free hydrosol. The hydrosol coating could be prepared by mixing this hydrosol with the crosslinking agent M(NH3)42+ (M2+ could be either Zn2+,Cu2+. Ni2+ or Co2+). It was supposed that in the soap-free acrylate hydrosol/M(NH3)42+ mixed system, before heating,M2+ in the form of M(NH3)42+could not react with the hydrosol(P-COO-)completely leaving some _COO-free to stabilize the hydrosol, and after heating(or curing),M2+ could be set free from NH3 ligand to join the coordination-crosslinking reaction with(P-COO-) forming network structure (P-COO-)n M2+.IR spectrographic analysis, fluorescence analysis and the linear sweep voltammetry plarogrphic analysis identified the existence of (P-COO-)nM2+ in the coating film. The crosslinking extent of the coating film was investigated by DSC and gravimetric analysis. All results indicated that the appropriate crosslinking agent was Zn(NH3)-2+ and the optimum curing condition was heating at 80℃ for 30 min. The crosslinking process of the hydrosol with Zu(NH3)42+ was examined by TEM. The kinetics of the crosslinking reaction has been studied preliminarily by DSC showing that the reaction activation energy was 34.0kJ•mol-1 and the order of reaction was 3.3, indicating that the crosslinking reaction may be a rather complex reaction.