In this paper, we study the Hamiltonian Ermakov systems using the method of form invariance. In terms of the form invariance of the Hamiltonian Ermakov systems,the generator of point symmetry transformations and the partial differential equations for the potential energy are obtained by comparing the coefficients of all monomials.The result indicates that under the point symmetry transformations,only the autonomous Hamiltonian Ermakov systems possess form invariance.