An index parameter called the maximum area shrinkage-cracking ratio (SCR) was proposed in this paper. It was defined as the ratio of the total area of shrinkage cracks of soil after drying to the initial surface area of the soil sample in a standardized mold. The effect of four factors namely, initial water content, initial sample thickness, mold surface roughness and test temperature were investigated using the soil samples from many different regions. After that, the reliability of using SCR to classify expansive soil was analyzed. Finally, the classification of expansive soil by SCR is proposed. The test results show that the initial water content and mold roughness have little influence on the identification and classification. When the sample initial thickness is limited to 8 mm, the influence can be ignored. The recommended drying temperature is 105℃. Besides, SCR is linearly correlated with the montmorillonite content and cation exchange capacity, which can reflect the nature of expansive soil; The linear correlations between SCR and standard moisture absorption water content and plasticity index indicate that it is highly reliable to identify and classify expansive soil using SCR. The maximum area shrinkage-cracking ratio test is simple and credible.