This experiment introduces a method of removing cobalt using a sulfuric acid-hydrogen peroxide mixed solution. It was observed by SEM that a large depth of corrosion pits appeared on the surface of polycrystalline diamond after cobalt removal at room temperature for 48h , and the cobalt phase was basically removed. The depth of surface cobalt removal was 164 μm and 172 μm, Through EDS, it can be determined that the residual cobalt content in the de cobalt layer is 0.93%, while the residual cobalt content in the non de cobalt layer is 7.64%. The results show that 87.83% of cobalt is dissolved by the mixed solution of sulfuric acid and hydrogen peroxide in the experiment. After the sample is cobalt removed, the hardness test is performed on it. Compared with before cobalt removal, the hardness changes little. The edge point hardness is the highest at 89.7 GPa, the center point hardness is the lowest at 81.26 GPa, and the average hardness is 86.25 GPa. The residual stress of the polycrystalline diamond sample was measured, and it was 483.91 MPa before cobalt removal and 330.35 MPa after cobalt removal, a decrease of 31.73%, indicating that cobalt removal can effectively reduce the internal residual thermal stress of PCD.