The invention relates to a hot air drying system. A drying device comprises a box body, a temperature sensor, a flow rate sensor and a conveyor belt. The conveyor belt penetrates through the box body, the temperature sensor comprises an inlet temperature sensor for measuring the temperature of hot air entering the drying device, the flow rate sensor is used for measuring the flow rate of air entering the drying device so as to calculate the flow of air entering the drying device, an air inlet pipeline temperature sensor and the flow rate sensor are in data connection to a central controller, and hot air guided by a fan enters the drying device through an air inlet pipeline to dry coal; the fan is in data connection to the central controller; and the central controller automatically adjusts power of the fan according to the detected coal supply quality in unit time so as to adjust the flow of hot air entering the drying device. According to the hot air system provided by the invention, the temperature of air inlet hot air and the coal supply amount of the drying device are linked together for the first time, so that an intelligent control relationship therebetween is established, and meanwhile, coal is dried by intelligently utilizing solar energy, so that the hot air drying system is energy-saving and green and environmental-friendly.