In this study, an automatic glycated hemoglobin (HbA1c) impedance measurement system (AHMS) is developed for the detection of HbA1c. The proposed device removes some of the drawbacks of common instruments for HbA1c detection (i.e., large, expensive, difficult to operate) by detecting the ratio of HbA1c to Hb. The method is label-free and requires only a small sample volume; no additional reagents are required. The manpower consumption and bulk of the instrument are also reduced. The method provides a simple way to analyze impedance deviation and effectively reduces the effort required by the operator. The ratios of HbA1c to Hb (4%-7%) are well distinguished, and the experiment is used to build a database for AHMS. To check the reliability of the proposed system, a sample test using three different ratios of HbA1c is applied in this study. The sample test uses HbA1c to Hb ratios of 4.7%, 5.6%, and 6.8%, and the determined experimental values are 4.93%, 5.8%, and 6.83%, respectively. The sample test has an accuracy of approximately 96.99%. Based on these results, the proposed system for detecting HbA1c through protein coverage is both effective and feasible.