Abstract: Sm, Nb co-doped La_1.7Sm_0.3Mo_2−xNb_xO_9−δ (LSMN, x=0.1~0.6)were prepared by solid state method using lanthanum oxide, samarium oxide and molybdenum oxide as raw materials solid electrolyte. The crystal structure and ionic conductivity of LSMN were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and electrochemical impedance spectroscopy. The results show that the grain size of LSMN is between 51.6 nm and 199.3 nm. After calcining at 700 ℃ for 8 h, the ultrafine powder with cubic structure can be successfully prepared, and the powder has high sintering activity. After sintering at 1100 ℃ for 10 h, the grains of the sintered body are tightly bound, the grain boundaries are clear, and the relative density is above 96%. The electrical performance analysis shows that the doping of Nd³⁺ ions can significantly improve the ion conductivity of LSMN; La_1.7Sm_0.3Mo_1.6Nb_0.4O_8.8 is sintered at 1100 ℃ for 10 h to obtain solid electrolyte, and the maximum ionic conductivity is 3.05×10⁻² S·cm⁻¹ at 800 ℃, its activation energy reaches 1.703 eV.