The invention relates to a method for performing constant-temperature flexible air separation after drying leaf silk airflow. The method comprises a leaf silk airflow drying process and a leaf silk air separation impurity-removing process and is characterized in that: new air at the inlet of a flexible winnowing machine is heated through high-heat-content process waste gas exhausted by a leaf silk airflow drying and humidity-discharging system, so that the temperature of the new air of the leaf silk winnowing machine is increased. The specific scheme is that: a high-efficiency heat exchange device is arranged before an air inlet of the winnowing machine and the air is preheated by the process waste gas of the airflow drying system, so that the air inlet temperature is increased, temperature difference between the air and the leaf silk is reduced, and the problem that the temperature is reduced quickly in the leaf silk air separation process is effectively solved. Compared with the prior art, the method has the advantages of completely utilizing the process waste gas exhausted by the system, increasing the temperature of new air entering the leaf silk winnowing machine, reducing temperature difference, effectively reducing influence on the quality of the leaf silk because the leaf silk is cooled quickly, reducing energy consumption of an air condition system in a workshop through outdoor air, and fulfilling three purposes.