In this paper, a new lensless digital holography system with short-coherent light source is designed for recording three-dimensional surface contour of reflecting micro-object. In the experiment, the different layers on the inner wall of a conical pore are recorded by changing the path length of object beams to record a series of sub-holograms for three-dimensional reconstruction. This makes the recording system compact and reduces the additional error in the recording. The measured longitudinal error is about 3.5%，with a lateral error of about 2.6%. Besides, the least squares polynomial fit method is used for the first time to carry out three-dimensional reconstruction with a series of two dimensional intensity images of a micro-object, which not only reduces obviously the complication of the three-dimensional reconstruction, but also can be used to carry out three-dimensional reconstruction of a micro-object with strong laser speckle noise, of which the phase images can not be obtained from the phase-unwrapping process.