PROBLEM TO BE SOLVED: To provide an analysis method of slag composition in which the slag composition can be determined rapidly with high accuracy in a refining field, and provide a refining method of molten metal in which an additive amount of solvent can be determined without excess or deficiency.SOLUTION: An analysis method of slag composition of the present invention includes the steps of: calculating emission intensity I(X)per unit content of the oxide of element Xin a slag sample with a clear chemical composition; generating plasma on the surface of an analyte by laser irradiation, and determining whether or not the laser irradiation is applied to the slag based on the emission intensity of the element in the plasma; calculating an apparent content of the oxide of the element Xin the slag of an analysis object when determined that the laser irradiation is applied to the slag of the analysis object; calculating a net content of the oxide of the element Xin the slag of the analysis object; and repeatedly
