The viscoelastic flow in a planar abrupt contraction was analyzed including the inertia effect, and the effects of inertia and viscoelasticity on the flow were studied. The Galerkin finite element method was employed as the numerical method. The constitutive model was the simplified Criminale–Ericksen–Filbey (CEF) model which expressed the extra stresses as an explicit function of velocity and deformation rate. We studied the effects of the Reynolds number, the Weissenberg number (the primary normal stress difference) and the elongational viscosity individually on the re‐entrant corner vortex and the entrance pressure drop. As a result, we found the following: (1) as the primary normal stress difference increases, the corner vortex grows up but the entrance pressure drop slightly decreases. (2) The inertia effect reduces the corner vortex produced by the viscoelasticity and increases the entrance pressure drop. (3) The flow fields are significantly influenced by the viscoelasticity in the low flow rate region but become to be dominated by the inertia with increasing flow rate. (4) Both the vortex intensity and the entrance pressure drop for the fluid with strain‐thickening elongational viscosity are larger than those for the fluid with strain‐thinning elongational viscosity.