The invention provides a nitrogen closed cycle drying method and device for drying polyacrylonitrile. The method comprises the steps that wet polyacrylonitrile filter cakes are sent to a micro powder drying machine and are dried and crushed at the place where the wet polyacrylonitrile filter cakes meet with the nitrogen which is heated to 250 DEG C by a nitrogen heater and an electric heater, and the dried material is sent to a bag-type dust collector for separation; the solid material is transported out by a rotary discharger; the dried material rotates and rises along with the hot nitrogen in a drying chamber to enter a washing tower, the nitrogen is washed and cooled by importing process water at 43 DEG C to a cooler, and the purified nitrogen and steam enter the downstream process from a tower bottom through a circulating pump, and then the nitrogen enters the nitrogen heater and the electric heater to be heated to 250 DEG C after being dedusted and boosted by a circulating fan and finally enters the micro powder drying machine, thus forming a nitrogen closed cycle drying system. By adopting the nitrogen closed cycle system and micro powder drying technology, the nitrogen closed cycle drying method and device achieve the purposes of drying the polyacrylonitrile, saving energy and reducing consumption. The nitrogen closed cycle drying method and device are safe and environment-friendly and the economic and social benefits of the enterprises are improved.