In this study linear polyether polyurethanes (PU) and sulfonated dimethyl fumarate (SDMF) were successfully synthesized and a series of novel solid polymer electrolytes, based on the complexes of PU and SDMF, were prepared. Fourier transform-Raman spectroscopy (FT-Raman), H-1-NMR, differential scanning calorimetry (DSC), atomic force microscopy (AFM), and complex impedance analysis were utilized to investigate the chemical structure, microscale morphology, and ionic conductive property of this system. Results show that the ionic conductivity of the PU/SDMF series increases with increasing temperature. In the salt concentration range investigated, there is a maximum ionic conductivity for the PU/SDMF system. When the molar ratio of the ether oxygen and sodium cation is about 24, the optimum compatibility between the hard and soft segments is realized and the highest soft-segment T-g is reached. A further increase in salt concentration causes the aggregation and precipitation of SDMF, and the decrease of the soft-segment T-g.