Abstract: In order to measure the surface topography of micro transparent objects quickly and effectively, a two-step phase-shifted digital holography system based on Mach-Zehnder interferometer was designed. The system used two identical CCDs to collect interferometric images at different distances at the same time. An optical phase shifting unit was used to form a π phase shift between the interferograms recorded by each CCD. Then the phase reconstruction algorithm was given by the space transfer function and Fourier transform of light. A two-step phase-shifted interferometric optical path was constructed. The microlens array was used as the object to be measured. The feasibility of the system was verified. The results show that, the system saves more than half of the time compared with the four-step phase-shifting method. It can achieve the phase reconstruction results consistent with the four-step phase-shifting method. This method is helpful to improve the efficiency of phase reconstruction.