We consider a gasmotion behind the front of a strong flat shock wave propagating along a flat surface, which, starting from a certain point, becomes perforated. The solution of Euler system of equations is constructed by a small parameter method. The characteristic ratio of gas densities at the shock front is chosen as a small parameter. An approximate analytical solution of the problem is constructed taking into account the terms of the first approximation. It is assumed that the gas flow through the permeable boundary is proportional to the pressure drop across it, which allows replacing the solution of the problem with the solution of a shock wave diffraction problem at an angle greater than. the structure of the flow in the perturbed region behind the diffracted shock wave is analyzed. The shape of the wave front is constructed for different values of determining flow parameters.