To detect defects on mirror-like object surfaces in the modern manufacturing industry, an automatic detection method based on phase measuring deflectormetry is proposed. The phase of the reflected image is extracted by combining the phase shift and Gray code, and defects are identified by an analysis of local phase irregularities. In addition, the phase extraction error that leads to false detection is analyzed. A wrapped phase period index correction algorithm is proposed to prevent period misalignment during the phase unwrapping. Therefore, accurate phase extraction can be assured through the phase unwrapping algorithm, and false detection is avoided. Experimental results indicate that the proposed method can accurately and reliably detect mirror-like surface defects.