Abstract: The effect of a catalytic curing agent with different contents on viscosity of a bisphenol-A resin was studied.Based on analyzing the curing characteristics of the resin system and the isothermal viscosity curves, an engineering viscosity model was developed. The model could be used effectively to predict the viscosity change of the epoxy system during a cure process, and could be used to indicate the regularity of viscosity change which is influenced by the content of the catalytic curing agent. The work is a basic study for processing simulation and process parameters prediction of composite manufacturing.