A novel carrier method to isolate out-of-plane displacement from in-plane displacement is presented. A reference is added to dual beam symmetric illumination ESPI system and shared by the two illuminations. The way to introduce carrier by tilting the test object enjoys high fringe visibility. When the object is loaded,the cartier will be curved due to the modulation of deformation of the object surface, The two illumination lights are used separately in experiment, With the carrier and the modulated carrier, two phase maps, which include out-of-plane and in-plane displacement, can be derived by Fourier transform. Theoretical analysis shows that out-of-plane displacement can be separated from in-plane displacement only by simple calculation of phase. This method has been proved to be feasible by a typical experiment using a centrally loaded clamped circular plate. Some results are offered,which show that the magnitude of in-plane displacement of the circular plate is one order lower than that of out-of-plane displacement.