The invention provides a method for preventing tobacco leaves from mildewing and rotting in the baking process of an airflow rising type bulk curing barn. An airflow in the bulk curing barn can be under the conditions of oscillatory internal cycle, oscillatory motion and staged one-way slow moisture discharging by utilizing a fan air direction change control system to change the airflow direction in the barn after 12 hours in a yellowing period, and normal airflow motion direction is recovered within about 48 hours. In an oscillatory period, one-time change of the airflow motion in the barn every 10 minutes is set, oscillatory internal cycle is performed for 2 hours, then oscillatory motion and staged one-way slow moisture discharging (effective discharging time is 0.5 hour) are performed for 1 hour, a heating and moisture discharging stage is executed, and the airflow in the barn is changed into a normally rising airflow. The other baking technologies of the method are same as conventional baking. The method makes the temperature and humidity of the tobacco leaves in the barn uniform, the large difference of a high-temperature zone and a low-temperature zone is relieved, formation of condensed water at the top of the barn is reduced, and accordingly the temperature and humidity difference and tobacco leaf mildewing and rotting caused by condensed water in the baking process are decreased.