Abstract: Gray method of tooth surface objects is one of the important methods to extract the gear interference image foreground region in laser phase-shifting interferometry. In view of the problem of limited measurement efficiency and limited accuracy caused by the manual threshold setting and neglect of different image edge features, a foreground region extraction method of gear interference image based on adaptive threshold was proposed. Firstly, the morphological characteristics of gear tooth surface and difference of each edge vertex were analyzed, and the image was divided into regions. Then, according to the changing rule of edge gray scale, the mask results were obtained by selecting qualified pixels through neighborhood window, so as to realize the foreground region extraction. Finally, the segmentation results of four groups of algorithms and traditional methods were compared according to five kinds of image evaluation indexes. The results show that the matching accuracy between the algorithm and reference results is improved by about 3.5%～4.5% based on the automatic image processing, the probabilistic rand index (PRI) is improved by about 3%～4%, the variation of information (VOI) is improved by 15%～25%, the global consistency error (GCE) is reduced by 2.5%～3.5%, and the final phase information accuracy is increased by 9 μm～15 μm. The results meet the requirements of accuracy, and the method can be widely used in foreground extraction of gear interference image.