Drying is a necessary post-harvest handling aspect of the grain and directly determines the final economic benefit of the grain. In order to solve the need for rapid temperature adjustment in the process of grain drying and the great fluctuate of heat source, a coaxial side-entry shell-shaped temperature-variable drying and mixing device was designed to cooperate with the variable-temperature control of the negative pressure dryer. In order to achieve high-efficiency and uniform air mixing, the guide vanes distribute cold air in the air rotating housing was radial mixing mode, and the valve opening was precisely adjusted by electro-mechanical linkage gear plate. In order to improve the accuracy of variable temperature control and the stability of mixed temperature, the relationship between valve opening and hot air temperature, fan frequency and system temperature difference was analyzed by neural network prediction and design method of regression experiment, and the air volume mixed control model of variable temperature mixing device was established. Based on the principle of large eddy simulation, the mixing temperature field of variable temperature drying mixing device was simulated by Fluent software. The distance of the best mixing effect was 26.85cm. The simulation results were in good agreement with the infrared thermal image verification diagram. The test results showed that the full range time of variable temperature control was 0.75s, the maximum value of variable temperature difference was 0.96℃, and the qualified rate of control was more than 84%. The output rice moisture content was in a reasonable range, and the quality of rice after drying was better, which can meet the production requirements. The results of the research provide a reference for achieving high quality, high-efficiency, energy-saving drying process and equipment design.