The plane problem of nonlinear elasticity for non-uniform plate with an interface crack is solved. The plate is formed by joining of two half-planes. Mechanical properties of half-planes are described by the model of John’s harmonic material. Application of this model has allowed using the methods of a theory complex functions and to obtaine exact analytical solution of a problem. The values of nominal stresses and displacements are founded. As an example the case of a free crack in plate subjected to constant stresses at infinity is studied. From exact solutions the asymptotics of the stresses and displacements have been constructed in a vicinity of crack tip.