A mobile heat pump drying system driven by a diesel generator was designed to meet the need of the agricultural mechanical harvest. A horizontal multi-room fluidized bed serves as the drying chamber, and a vapor compression heat pump (R134a as refrigerant) supplies heat for this system. Heat exchangers are installed along the air duct to recover the waste heat from the cooling water and flue gas in the diesel generator, which increased the primary energy ratio(PER).A mathematical model for the system composed of fluidized bed, heat pump and diesel generator was also presented. Modeled results showed that the value of drying system’s specific moisture extraction rate (SMER) was firstly up and then down, with air temperature in the range of 60～90℃, and reached a peak value around 70℃. Testing experiments of the prototype dryer showed that under the designed conditions, the mean coefficient of performance (COP) is 4.66, PER is 1.09 and SMER reaches 3.08 kg/(kW?h). The model is in good agreement with experimental results, and this grain dryer is significantly energy saving.