The typical two-step phase-shifting algorithm cannot get rid of the problem in phase unwrapping processing, which is caused by the uneven distribution of intensity and the uneven reflectivity of objects. Aiming at the problem, a intensity formula, reflecting the reflectivity of the objects, is adopted, based on the analysis of 90° phase shift. The intensity data was operated directly. Then, according to the triangle theory, a algorithm was presented to get the half angle of wrapped phase. At last, three-dimensional shape information of the tested object was decoded, according to the relationship between height and difference of phase. This method avoids the errors caused by the method used to get the maximum or minimum value. The results of the proposed method are compared with those of the typical four-step phase-shifting algorithm and the two-step phase-shifting algorithm. When the surrounding intensity can be ignored or weak, its error is ±0.2 mm. It is better than resutls of typical two-step phase-shifting algorithm, close to results of accepted low-error four-step phase-shifting algorithm.