The invention discloses a preparation method and application of HR3C steel microstructure corrosive liquid after 50,000 hours of service. The HR3C steel microstructure corrosive liquid comprises 4.5-4.7g of ferric trichloride, 53-55ml of hydrochloric acid analytically pure, and 100ml of water. According to the preparation method and the application of the HR3C steel microstructure corrosive liquidafter 50,000 hours of service, the morphology of an HR3C steel microstructure after 50,000 hours of service can be clearly showed by one-time corrosion, the grain boundary corrosion degree is easy tocontrol, precipitated phase morphologies such as chain-like and large-grained M23C6 on a grain boundary are particularly and completely showed, and details of the precipitated phase morphologies suchas granular and rod-like Nb(C,N), M23C6 and the like are clearly showed in a crystal; and the corrosion effect is real and stable, good reproducibility is achieved, and the preparation method is an ideal corrosion method for the HR3C steel microstructure morphologies after long-term high-temperature service.