Abstract: The physiology-biochemistry characters of step-temperature yellowing treatment were studied during bulk curing process by using the electric-heated flue-curing barn. The results showed that two obvious amylase activity peaks of step-temperature yellowing treatment appeared in yellowing stage and leaf drying stage, and amylase activity of step-temperature yellowing treatment was higher than 38℃ yellowing treatment. Polyphenol oxidase (PPO) activity of all the treatments decreased before 7-8 tenth yellow, then it displayed the trend with first increasing followed by decreasing after 7-8 tenth yellow for leaves during curing. And polyphenol oxidase activity of step-temperature yellowing treatment had a smaller variation range, and it was more relatively stable. chorophyll and carotinoid content of step-temperature yellowing treatment declined more than 38℃ Yellowing treatment. Starch of step-temperature yellowing treatment had a faster degradation, and its starch content was less than 38℃ Yellowing treatment during curing process. The step-temperature yellowing treatment was beneficial to increase the accumulation of total sugar and reducing sugar. The total nitrogen and nicotine contents of cured leaves of step-temperature yellowing treatment rose slightly, which was similar to 38℃ yellowing treatment. The step-temperature yellowing treatment was beneficial to improving the quality of tobacco leaf by the comprehensive performance of physiology-biochemistry.