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In drying of paddy, the mechanical stress inside paddy kernels is caused by moisture content gradient and glass transition temperature (GTT). The stress results inside kernel crack during the milling process. The hot-air drying method was employed to investigate the effects of stepwise changes of air temperature determining GTT on stress cracking index, head rice yield and drying duration of paddy. To achieve the objectives, the concepts of glass transition for paddy and temperature and moisture distribution of material layer were determined by using numerical modeling method. The center combination tests of three-factor with five-level were employed to analyze and optimize the parameters of drying process for paddy under constant temperature. The surface temperature, initial moisture content of paddy and the hot-air speed were selected as the influencing factors. In terms of the stepwise changes of air temperature, the drying experiments were conducted at temperatures above the GTT based on the optimal parameters determined by constanttemperature drying process. The rising amplitudes of temperature were 5℃, 10℃ and 15℃, respectively. The results showed that the GTT of paddy was negatively correlated with its moisture content. The optimum parameters of constant-temperature drying were developed as temperature was 47℃ and the initial moisture content was 22.0% for paddy, and hotair speed was 0.50m/s, respectively, and the evaluation indexes were as follows: the stress cracking index was 70, head rice yield was 57.67%, and process duration was 195min, respectively. Compared with the constanttemperature drying, under the stepwise changes of air temperature of 5℃ and 10℃, the quality of paddy dried was improved as the stress cracking index was decreased by 20 and 10, the head rice yield was increased by 12.6 pencentage points and 7.7 percentage points, respectively, and drying duration was shortened by 30min and 60min, respectively. Therefore, the stepwise changes temperature of hot-air drying can improve the drying efficiency and quality of paddy based on glass transition theory. The results may provide references for the hot-air drying process and quality control of paddy.