Electrodes can absorb moisture easily so that the diffusible hydrogen is quite high in the weld bead. Fe3O4 powder is used to promote the reaction of myristic acid and the electrode surface, and reduce the diffusible hydrogen, because of its excellent microwave absorption property. Electrodes are immersed to the light petroleum solution which contains myristic and Fe3O4 particles, then they are put into the microwave oven and become water-resistant . The results of FT-IR and SEM microscope indicate that Fe3O4 powder absorb microwave and melt myristic acid to form the water-resistant film. The best ratio of myristic acid in the petroleum ether is 18% and the diffusible hydrogen of the deposited metal of microwave treated electrode decreased to 83% of the untreated electrode.