Since the involute profile error of a gear shaft influences its transmission performance, it is desirable to accurately and quickly measure its involute profiles. With the advantages of low cost, universal applicability and in situ detection, a vision measuring method for multiple involute profiles of a gear shaft is developed only using one image in this study. The base circle radius and initial position angle of the involute are obtained by geometrically fitting the involute profile. The correctness and reliability of the method are tested by measuring the pitch deviation of the gear shaft; a specialized experiment is carried out; and the factors affecting the measurement accuracy also are analyzed.