Solid oxide fuel cell (SOFC) has been extensively identified as one of the most promising energy conversion technologies characterized by high efficiency and environmental friendly. Low-temperature SOFC is the main direction of development of SOFC. Exploitation of new electrolytes with excellent performance is urgently required to develop low-temperature SOFC (400～600 ℃). Functional composite electrolytes are regarded as the promising electrolyte materials, and the ion conductivity is significantly improved compared to single-phase materials. The recent progress in composite electrolyte, the characteristics, type and conductive mechanism of composite electrolyte were introduced in the paper.