The invention discloses a granular heat-preserving covering flux for hot metal in steelmaking, and relates to a treatment agent added into a ladle for preserving heat on the surface of hot metal for steelmaking. The granular heat-preserving covering flux is characterized in that: the heat-preserving covering flux is prepared from expanded vermiculite, wollastonite, bauxite, iron ore concentrate and coke powder, and comprises the following components in percentage by weight: 30 to 35 percent of SiO2, 15 to 21 percent of (CaO+MgO), 7 to 12 percent of Al2O3, 3 to 5 percent of Fe2O3, 15 to 20 percent of C, and the balance of impurities; and the raw materials are ground, sieved, mixed, mixed and stirred, dried, cooled, and weighed and packaged at normal temperature and normal pressure. The granular heat-preserving covering flux has the advantages that: the granular heat-preserving covering flux has good slagability and spreadability, is conveniently adsorbed by inclusion, contains a heat-generating agent and an oxygen supplying agent so as to facilitate melting per se and reduce iron sticking and ladle sticking; the expanded vermiculite and the wollastonite regulate components of the heat-preserving covering flux, and have expanding and heat insulating functions, and good heat preservation property; the MgO regulates the alkalinity and reduces the adhesion of the heat-preserving covering flux with a ladle lining so as to facilitate cleaning slag in the ladle; and the heat-preserving covering flux is granular and greatly reduces dust pollution.