Abstract: The porosity defects in the heavy ingot can be treated as compressible material due to their similar physical property and deformation characteristics. Aiming at the forging process of large Cr5 typed steel backup roller, the paper established a non-linear FEA model for compacion process of porosity defects by means of the rigid-plastic finite element method for compressible material. From the numerical simulation results, the influence of the initial porousity, tool width ratio, contact friction coefficient and reduction on the defects collapse was disccussed. By preparing artificial porosity defects which sinter the deoxidized ferrous powder inside a cylinder sample, the forging experiment was carried out on the platform of Gleeble-3500. And the numerical simulation results were verified by the experiment through metallographic observation and compaction analysis of the porosity defects. The research conclusions provide a theoretical foundation for designing and optimizing the forging technology parameters.