Polyurethane/vinyl ester resin interpenetrating polymer networks (PU/VER IPN) were synthesized at room temperature by polymerizing ethyl acrylate as VER’s comonomer and simultaneous interpenetrating process. The curing process of the IPN was dynamically traced and semi-quantitatively analyzed by Fourier transform infrared spectroscopy (FT-IR).The result shows that the network of PU was formed firstly and completely because of different polymerization mechanism of the networks and the influence of viscosity. The results of the compatibility of the networks detected qualitatively by differential scanning calorimeter (DSC)

atomic force microscopy (AFM)and transmission electron microscope (TEM)showed that the phase range of dual continuous simultaneous interpenetrating networks obtained was in nanometer scale.A single glass transition temperature (Tg)，appeared for the IPNs with the component ratios of 80/20 and 70/30 and the compatibility between polyurethane and general vinyl ester resin was improved.Compatibility factor (θ) was obtained through calculation of Tg detected by DSC and theoretical Tg and the compatibility of the networks was further detected quantitatively.