Abstract: Aim To study the factors affecting the mechanical properties of highly plasticized polyurethane(PU)/poly (glycidyl methacrylate) (PGMA)simultaneous interpenetrating network(SIN) and find the recipe with best mechanical properties. Methods Samples with different recipes were prepared and their mechanical data were obtained by using tensile test and dynamic mechanical analysis. Results and Conclusion The tensile strength and elongation of SIN change non monotonically as the composition ratio of PU to PGMA varies, their maxima would be obtained with PU content ca.60%. The introduction of crosslinker of PGMA and inter network grafting reagent into the system will increase the corsslinking density of the system, which results in that the tensile strength was elevated and the elongation was decreased.