Tool parameters play a vital role in the mechanical interlock formation during the at clinching process, to understand the in uence of tool parameters on the interlock formation, the nite element software DEFORM-2D was used to build the numerical model of the at clinching process, and the numerical model was veri ed by the experiment. The in uences of the punch radius, punch llet radius, and blank holder radius on the interlock formation of the clinched joint were investigated using the numerical model. Then, the relationship between the punch radius and blank holder radius was studied. The results showed that the interlock gradually increases with the increase of the blank holder radius, after that, the interlock begins to decrease. To maximize the interlock, the punch radius and the blank holder radius should be increased simultaneously. It can be concluded that the blank holder radius and the punch radius should keep in a linear relationship when designing the geometric dimensions of the at clinch tools, which can promote the application of at clinching process in car body manufacturing.