Steady characteristics of an aerofoil in a two-dimensional subsonic shear flow are analyzed by the singularity method. First, on the assumption of small disturbances, fundamental solutions which represent a vortex and source are introduced from an equation for perturbed pressures. The solutions have two kinds of singularity: one is the same singularity as in a uniform flow and the other is logarithmic. Then, the thin aerofoil theory is applied to an aerofoil with a thickness. A source distribution is determined by only a thickness of aerofoil. However, a vortex distribution is determined by solving the integral equation, which includes the interferential term between the thickness and the vorticity of a shear flow. In a shear layer and a jet flow, lift forces acting on a flat plate and a Joukowsky symmetrical aerofoil are calculated. A flat plate in a faster part of the shear flow has less lift than that in a uniform flow. Lift on a Joukowsky aerofoil is strongly influenced by the vorticity of the shear flow.