Failure and slip on the wall in the straight pipe were studied for highly filled suspension (HSF) of kaolin‐water including additives. To visualize the deformation of HFS, red mark lines were inserted. Complete slip between HSF and solid wall was observed. It was confirmed that Coulomb’s criterion was valid for the failure between flat wall and HSF, and was different from that in the bulk suspension. The equilibrium equation between the failure shear stress at the wall and the extrusive pressure by piston was derived on the assumption that the extrusive pressure was equal to the axial stress at the wall. The prediction, which showed the variation of extrusive pressure along the axial direction, was in good agreement with the experimental result. It was also shown that the increase of wall stress with slip flow velocity after the failure was equal to the superposed friction resistances of motion to the static failure stress.