Based on the second law of thermodynamics, a heat exchanging dehumidification system was designed. It mainly composed of a hot-swappable ventilator and an environmental monitoring system. The goal of greenhouse heat recovery was achieved by forced convection of the fresh air outside the greenhouse and the air in the greenhouse to lower the humidity, and increasing the temperature of fresh air by heat exchanging. The parameters of internal environment of greenhouse and working state of dehumidification system could be acquired remotely by the monitoring and control system, and the humidity of the greenhouse could be regulated real-time. This system was applied to the greenhouse of tobacco floating-seedling system, results showed that the heat exchanging dehumidification system had good performance of dehumidification. Compared to the normal greenhouse, the average humidity of experimental greenhouse with the average rate of heat recovery of 59.35% decreased 6.7% with an average increase in stem height stem of 0.4 mm and stem diameter of 0.6 mm.