The invention discloses a low-temperature dehumidification combined hot air drying device. The low-temperature dehumidification combined hot air drying device comprises a drying chamber 1, a primary air return chamber 2, a secondary air return cooling chamber 3, a temperature rise air supply chamber 4, a box 22 and a control host 25. Through a secondary heat exchange system composed of a plate heat exchanger and a surface cooler, the evaporation temperature of a refrigerant is reduced, and the problems of compressor damage and system stability due to the fact that refrigerant reflux temperature is too high are solved. A closed cycle heat pump drying unit can be free from the influence of external climatic conditions and realize stable and efficient operation all the year round. Combined hot air drying can reduce the energy consumption in the preheating process at the initial stage of material drying, and the mixed waste heat of "secondary air return" and "primary air return" can improve the energy utilization efficiency of a heat pump system. A full-automatic control system can intelligently control an electric valve according to temperature, relative humidity and pressure difference, so that waste of heat source is eliminated to the greatest extent, and optimal utilization of energy in the whole drying process is achieved.