The concept, backgrounds, progresses of academic research and industrial applications of digital twin (DT) are first introduced. Then, based on the concept pf DT, a new shop-floor paradigm towards smart manufacturing, named digital twin shop-floor (DTS) is proposed and discussed. The architecture, system composition, running mechanism, and enabling key technologies of DTS are investigated. Then the theories and technologies for cyber-physical fusion based on DT are discussed from four aspects, including physical fusion, model fusion, data fusion and service fusion. At last, the related practical researches of DT from the DT research group at Beihang University are briefly introduced.