Abstract: The coarse grain was found in heat affect zone(HAZ) of SUPER304H steel produced by a domestic plant,whereas the corresponding grain size of the same product of another plant abroad was homogeneous and fine. The phenomena was investigated by means of optical microscopy(OM),scan electronic microscopy(SEM) and electronic microscopy probe analysis(EMPA). The Cr23C6 phase was found in HAZ of the product abroad. The precipitation of the Cr23C6 phase refrained from the growth grain boundary in the second thermal cycle,but also would lead to a bad anticorrosion property. The precipitation of Cr23C6 phase was related to the difference of element composition and welding procedure.