In this study, a two-stage system comprising a heat pump evaporator integrating heating and dehumidification was designed. Evaporator 1 pre-dehumidified the air and evaporator 2 recovered the heat from the remaining air treated by evaporator 1. The low-humidity air condensed by the two-stage evaporator could be used for drying materials directly. The evaporator could obtain different heating and drying conditions by adjusting the air velocity of evaporator 2. This study established a model for heat and mass transfer involving a two-stage evaporator under wet conditions. The evaporator's heat and mass transfer attributes were simulated, and the simulation results were found to be in high conformity with the experimental values. The relative error of temperature was -3.0-3.0%, and the relative error of humidity was -10.0-3.0%. The liquid film was mainly distributed at the beginning of the fins and decreased along the length of the fins. The relative humidity of the air increased by 10.0%, the thickness of the liquid film increased by 65.0%, and the temperature of the liquid film increased by 1.5%. The air velocity increased by 1.0 m s(-1), and the liquid film temperature decreased by 6.7%. The mass transfer coefficient increased with increasing air velocity, while it decreased with increasing air relative humidity. The air velocity did not affect the latent heat ratio (LHR) of the evaporators. Moreover, the LHR of evaporator 1 was less than that of evaporator 2. Increasing the air velocity of evaporator 2 could provide more heat for the refrigerant, whereas decreasing the air velocity of evaporator 2 could increase the dehumidification capacity of the evaporator to unit air of mass and provide low-humidity air for the drying box.