Abstract: With wire feeding in site test of adding Y-base heavy rare earth in 51CrV4 spring steel, to improve and control the size and morphology of inclusion, through field sampling, by large sample electrolysis, metallography, examination scanning electron microscopy and spectroscopy analysis means of observation, analyzed the typical inclusions of casting and rolling material in 51CrV4 spring steel. The practice results show that The addition of yttrium based heavy rare earth steel in spring steel has obvious effect on inclusion modification, the mainly inclusions exist in RE₂O₃, RE₂O₂S, RE₂S₃ and other rare earth inclusions, generation of rare earth compound inclusion size in 2~4μm, and a regular spherical shape; large inclusions in detection not found rare earth elements, but the large inclusions morphology than inclusions without rare earth is more rounded and spherical, and the size is more refined.