The affecting laws of boron and silicon on structure and properties of Fe-based superalloy were studied by analyses of scanning electron microscope (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Proper content of boron could not only purify the matrix and restrain the polymerizing and growing of carbides effectively, but also promote the forming of secondary precipitate of borides, which dispersed in form of micro particles to strengthen grain boundaries and enhance the heat strength for Fe-based superalloy. Boron was an adverse element to high temperature oxidation resistance. Silicon could toughen the matrix by solid solution strengthening. Overfed silicon in alloys caused great dropping of strength and toughness. The component of SiO2 endowed the oxide scale with flat and compact structure, fine and even grains, and few exfoliating. The optimum contents of boron and silicon in Fe-based superalloy are 0.02wt.% and 1.5wt.% respectively by comprehensive consideration of high temperature mechanical properties and oxidation resistance.