A method for three-dimensional displacement measurement by separating out-of-plane displacement from in-plane displacement is presented. A reference laser beam is added to dual beam symmetric illumination electronic speckle pattern interferometric (ESPI) system and is shared by the two illumination beams. The two illumination beams are used separately in experiment for the displacement measurement. Then two phase maps, including out-of-plane and in-plane displacement, are obtained with phase shifting technique, then one of which is calculated by reversed phase calculation method. Theoretical analysis shows that subtraction of the phase maps can greatly decrease electronic noises, separate out-of-plane displacement easily from in-plane displacement and complete three-dimensiomal displacement measurement. The principle of the method is presented and proved by a typical three-point-bending experiment.