Herein disclosed are a surface topography measuring system and a method thereof. The method comprises the following steps: dividing a test beam into a first sub-beam, entering a reflecting mirror along a first axis, and a second sub-beam, entering an object surface along a second axis; moving the reflecting mirror for reflecting the first sub-beam at different positions on the first axis to generate N reflected beams; generating an object reflected beam, related to the second sub-beam, reflected from the object surface; generating N images, related to the N reflected beams and the object reflected beam, and each of the N images having a plurality of interference fringes; analyzing the interference fringes in each of the N images to calculate N curve formulas; calculating a surface topography of the object surface from the N curve formulas.