The present invention relates to a method for analyzing the molecular weight of each polymer comprised in a polymer compound, and an analysis system used therefor. More specifically, the present invention relates to an analysis method of components of polymer compounds and molecular weight by component using a system in which size-exclusion chromatography (SEC)-pyrolysis gas chromatography (Py-GC)-mass spectrometry (MS) are connected in series and to an analysis system used in the method.