A novel method for isolating out-of-plane displacement from in-plane displacement was presented.A reference was added to dual beam symmetric illumination electronic speckle pattern interferometry(ESPI) system and was shared by the two illuminations.The two illumination lights were used separately in experiment.Then two phase maps,which include out-of-plane and in-plane displacement,can be obtained with phase shifting techniques.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 feasible in typical three-point-bending experiment.