Abstract: In order to obtain phase information, many unfavorable factors such as noise, breakpoint and under sampling must be overcome. Aimed at too low sampling frequency and high fringe density, the root cause of the undersampling problem, unwrapping algorithm based on segmentation and zooming principle was introduced. After enlarging interference fringe whose density is too high by interpolation method, the phase was unwrapped. The simulation and experimental results show the feasibility of the proposed algorithm. It turns out that it is an effective unwrapping algorithm for undersampled wrapped phase.