The existence of the yield surface in the squeeze film flow of viscoplastic fluids was investigated by finite element simulations. In the case of Bingham fluid, the yield surface does not exist within the squeezing flow field as long as the squeezing process continues. When the bi-viscosity model is used as approximate constitutive equation of viscoplastic fluids, various shapes of the yield surfaces which have been proposed by previous researchers are observed depending on the squeezing speed and the value of γ（=μ_p/μ_r）. But, eventually the yield surface disappears as the model approaches to Bingham model.