Abstract: 10—30d extended-range forecast (ERF) is a forecast “seam” between traditional weather forecast and short-term climate prediction. It has become an important research direction for the development of international weather-climate seamless forecast system in the last decades. Some national or international weather-climate forecast centers have made preliminary achievements on ERF research and application based on MJO. In this paper, according to latest studies related to associations between MJO and weather or climate, starting from basic features of MJO, development of MJO monitoring and ERF application are chiefly introduced. The developments mainly include: ERF of MJO and operational application of MJO in ERF of heavy rainfall, typhoon, cold wave and disasters. Finally, this paper discusses the developing trend of ERF based on MJO in the future.