Abstract: The grain size morphology and grain boundary carbide precipitation of NC30Fe (Inconel 690) alloy after thermal treatment under different erosion conditions were studied by means of optical microscope and scanning electron microscope. The results show that with the new erosion agent-mixed solution of hydrochloric acid and ethanol (volume ratio of 1∶1) with a small amount of hydrogen peroxide, the grain size morphology and grain boundary carbide precipitation of the alloy could be clearly displayed, and compared with the traditional erosion agents, the new one has the advantages of simple and convenient operation, safety, reliability, short erosion time, high efficiency and high success rate.