To detect the abnormal quality of smooth surfaces under standardized quality control, a single-pixel detection theory about the abnormal reflectivity of a flat surface is proposed. The proposed method uses a single-pixel detector and only needs to project a single frame of structured light (illumination design). First, the radiation flux distribution of a single-pixel detection about the abnormal reflectivity of a flat surface is derived. It is shown that under uniform illumination conditions, the spatial distribution of the radiation flux to the detector is nonuniform. Thus, a special illumination design can achieve the uniform radiation flux distribution and convert the abnormal reflectivity distribution of a flat surface into the cumulative reflectivity anomaly (or total radiation flux anomaly). In the experiment, the corresponding detection device is designed. The radiation flux distribution on the flat surface to the detector under uniform illumination and the illumination design for achieving uniform radiation flux distribution are numerically calculated. They are consistent with the actual results. Under the illumination condition of uniform radiation flux distribution, the total radiation flux of seven types of qualified ceramic tiles and the abnormal total radiation flux caused by two kinds of surface defect—cracks and scratches were investigated. The results showed that the two surface defects lead to significant changes in the total radiation flux. The effectiveness of the theory and feasibility of the technology are preliminarily verified.