This paper studies a steady axisymmetric flow in a constricted rigid tube. A shear-thinning fluid modelling the deformation-dependent viscosity of the blood is proposed. The motion equation is written in vorticity-streamfunction formulation and is solved numerically by a finite difference scheme. The flow pattern with the distributions of pressure and shear stress at the wall are computed. The dependence of the flow on the dimensionless parameters has been investigated and differences from the Newtonian case are discussed.