The solid electrolyte Ce_0.8Sm_0.2-xPr_xO_1.9 (x=0.02 ~ 0.08) was prepared by sol-gel method. The microstructure and electrical properties of solid solution were characterized by X ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy (Raman) and AC impedance spectroscopy. The results of XRD analysis show that samples calcined at 800 oC for 4 h possessed single-phase cubic fluorite structure, and the average grain size is between 35-46nm. The AFM images showed that the samples were spherical and distributed evenly. After the incorporation of Pr ions, the voids of the samples decreased obviously. When the doping amount was x=0.08, the grain boundaries were formed with small particles, and the grain size was between 2~8μm. The results of Raman show that Ce0.8Sm0.2-xPrxO1.9 is a cubic fluorite with oxygen vacancy, and the doping of Pr ions is beneficial to the formation of oxygen vacancies. AC impedance spectra indicated that the conductivity of Ce_0.8Sm_0.2-xPr_xO_1.9 increases with the increase of Pr-doping, and the activation energy decreased.