A novel method based on windowed Fouri er ridge for separation of out-of-plane displacement from in-plane displaceme nt is presented and applied to the separation of multiple interference phases in digital holographic interferometry.Firstly,a single laser light source is used to illuminate the te sted object symmetrically to its surface normal,and a single reference beam is u sed in conjunction with the diffusely scattered object beams to record the hologram at the CCD plane.Two fra mes of off-axis hologram before and after object deformation are captured by CC D.Then,Fresnel diffraction integral reconstruction provides two complex object wave-fields before and after object deformation,and the interference field can be obtained by the conjugate mutiplication of two fr ame reconstructed complex object wave-fields.Windowed Fourier ridge and amplitude discrimination criteria are allowed to separate multiple interference phases which carry the information on multidimens ional deformation corresponding to the object beams with different sensitivity directi ons. Out-of-plane displacement can be separated from in-plane displacement only by simple numerical calculation of multiple interference phases.Finally,the experiment is conducted to prove the validity of the proposed method.A fully-clamped circular aluminum disk with a point load and in-plane rotation along its normal is chosen as a specimen,and i ts three-dimensioal (3D) displacements are successfully measured by the proposed method.The feasibility o f proposed algorithm is demonstrated by the experimental results.