Combining stroboscopic imaging and phase-stepping microscopic interferometry,a micro-electromechanical system(MEMS) out-of-plane measuring method based on compensation of in-plane motion is established.First,it can automatically acquire interferograms at different quasi-static positions in moving periods of MEMS structures with phase-stepping microscopic interferometry technology.Then,bright-field images at different quasi-static positions can be gained from interferograms by image processing to measure in-plane motions of MEMS structures.Finally,out-of-plane motions of MEMS structures can be compensated by inplane tests results,called as double-phase unwrapping,to complete measurements of MEMS out-of-plane motions.Experimental results indicate that the measuring resolution of in-plane tests is u to 0.01 pixel,and the measuring repetition of static out-of-plane tests is 0.52 nm.It can satisfy the measuring requirements of MEMS out-of-plane motion along with in-plane motion.