A polyurethane based on unsaturated polyesters (PUP) was prepared, which can be cured and cross-linking reaction under room temperature. The polyurethane-based resin exhibited excellent endurance to acid and base relative to traditional unsaturated polyester resin. Different content and particle size of aluminum hydroxide particles were added into the PUP to improve the properties of final materials. Experiment results showed that proper content and size of aluminum hydroxide particles can improve the mechanic properties, thermal stability and electrical insulation of PUP materials to some extent. Such result was confirmed by the fracture morphology of the samples because of the well dispersion of aluminum hydroxide particles into PUP phase.