The invention provides a heat preservation device of a ventilation pipeline. The heat preservation device is characterized in that the ventilation pipeline of a multi-layer structure, an air distribution collection device, an air supply pipe, an air return pipe and an air cooler form a loop; the multi-layer structure comprises a heat preservation layer, a cooling layer and a ventilation pipe fromoutside to inside sequentially; the cooling layer, the air distribution collection device, the air supply pipe and the air return pipe form an airtight air circulation system; and the heat preservation layer communicates with the air distribution collection device and the air supply pipe. According to the invention, the heat preservation device is applied to cooling of a long-distance tunnel and executes sectional automatic control on heat preservation of a tunnel cooling ventilation pipeline; and the structure is concise, mounting is convenient, maintenance is convenient, loss of refrigeration capacity is low, the cooling effect is good, and networking is flexible, intelligent and reliable.