Depending on the size of sets, a wrapped phase map is unwrapped by either region or pixel. In region phase unwrapping, the jump point threshold value is adjusted to search the region boundary after filtering a wrapped map with higher noise and then phase unwrapping ±2nπ in each region without filtering. The latter compares if the phase difference of adjacent pixels is greater than π as a reference for determining pixel point ±2π to perform phase unwrapping point by point. Although the former unwraps phase by means of boundary search and the latter with the phase difference of adjacent pixels, phase unwrapping errors occur in both cases in detecting surface cracks on materials as data on both sides of a crack are discontinuous. This paper proposes a solution for phase unwrapping on discontinuous surfaces by means of crack search and marking with region assembly phase unwrapping technology to locate boundaries in both region splits and crack splits and further extends the scope of application of region assembly phase unwrapping.