In　this　paper,　we　extend　the　well-known　Melnikov　method　for　smooth　systems　to　a　class　of　periodic　perturbed　piecewise　smooth　planar　system.　We　assume　that　the　unperturbed　system　is　a　piecewise　Hamiltonian　system　which　possesses　a　piecewise　smooth　homoclinic　solution　transversally　crossing　the　switching　manifold.　The　Melnikov-type　function　is　explicitly　derived　by　using　the　Hamiltonian　function　to　measure　the　distance　of　the　perturbed　stable　and　unstable　manifolds.　Finally,　we　apply　the　obtained　results　to　study　the　chaotic　dynamics　of　a　concrete　piecewise　smooth　system.