This research studied the rheological properties of the RTM resin system used in the cover of launch box, and established an isothermal chemical rheological model which predicted the sustaining time of the low-viscosity platform at different temperatures, providing a theoretical basis and quality assurance for the RTM process. The dynamic viscosity and static viscosity of the resin system was tested by rotational viscometer. Isothermal viscosity characteristics and the isothermal chemical rheological model were studied by double Arrhenius equation. Viscosity characterization showed that the viscosity of resin system was increased over time, and the higher temperature was, the faster the increase of viscosity was. The isothermal chemical rheological model equation was established . Theoretical simulation viscosity values of isothermal chemorheology model was in consistency with experimental results and predicted that the resin system would exhibit a low viscosity platform between 50~90 ℃, which met requirements of RTM process.