In order to solve the problems of high drying energy consumption, serious waste heat pollution and poor drying quality caused by traditional grain drying, a continuous grain vacuum drying system was proposed. An open absorption heat pump was used in the system to recycle the water vapor and its latent heat of vaporization generated during the grain drying, so this system has the dual advantages of low temperature vacuum drying and energy saving of the heat pump. Based on the experiments of continuous vacuum drying drum, a continuous vacuum drying system based on open absorption heat pump was designed. The mathematical model of matter and energy conservation of the system was established. The whole system process was modeled by Aspen Plus software, and the effects of drying pressure, solution heat exchanger efficiency, heating temperature and dilute solution concentration on the coefficient of performance(COP) and drying energy consumption were analyzed. The results show that under the design condition, the COP is 1.7285, and the drying energy consumption is 3 346.92 kJ/(kg·H20), which reduced 37% of the current energy consumption of the traditional grain dryer. Improving the efficiency of the solution heat exchanger, reducing the heating temperature and reducing the concentration of dilute solution can improve the COP and reduce the drying energy consumption.