The invention discloses a flux for reducing a fine coal gasification ash melting point temperature and a use method thereof and belongs to the field of fluxes. The flux is papermaking sludge, contains organic matters, has air-dried base heat of 800-1000 kcal / kg and alkaline oxide mass content more than 50% and comprises, by mass, 40-56% of CaO, 3-12% of MgO, 3-12% of Al2O3, 9-15% of Fe2O3, 14-20% of SiO2, less than 3% of SO3, less than 0.8% of TiO2, less than 1% of each one of alkali metal oxides and a small amount of impurities. The use method of the flux comprises that when a raw material coal deformation temperature is less than 1450 DEG C, a flux use ratio is in a range of 6-15%, and when the raw material coal deformation temperature is higher than 1450 DEG C, a flux use ratio is in a range of 15-30%. The flux can effectively reduce a coal ash melting point, realize resource utilization of papermaking sludge waste and realize utilization of papermaking sludge heat.