Abstract: The composite electrolyte La_1.7Sm_0.3Mo_1.8W_0.2O_9-δ(LSMW)-LaAlO₃(LAO) was prepared by solid-state method with a molar ratio of 10∶0, 9∶1, 8∶2, 7∶3, 6∶4, and 5∶5, respectively. The microstructure and ion conductivity of LSMW-LAO composite electrolyte were studied. The experimental results show that when sintered at 850 ℃ for 3 hours, the relative density of the composite electrolyte is above 95%, and the sintering shrinkage rate is below 3%, indicating high sintering activity. The ion conductivity of LSMW-LAO composite electrolyte decreases with the increase of LAO dosage. At 800 ℃, when the molar mass ratio of LSMW and LAO phases is 9∶1, the composite electrolyte has the highest ion conductivity, reaching 0.0341 S·cm⁻¹ and an activation energy of 1.323 eV. It is expected to become a solid electrolyte with industrial application prospects.