Abstract: Abstract: In order to reveal the change rule of grain moisture content in deep bed drying, guide the design of drying technology, and realize real-time tracking and regulating the drying process, as well as improve the drying quality and reduce the energy consumption. Based on the moisture diffusion model of thin bed drying process and the mass conservation equation of deep bed drying process, as well as the state function and irreversible thermodynamics analysis method, the basic function of deep bed grain drying was set up and solved, and the analytical formula of the distribution of grain moisture content and drying rate in the drying methods of concurrent flow and counter flow, cross flow and standing drying were obtained. The result showed that the drying rate experienced the continuously decreasing process inside the concurrent flow deep bed drying, and the maximum point occurred at the beginning of the drying, that said the moisture content decreased quickly, and the late changed extremely smooth in the hot air inlet position. In counter flow deep bed drying, the drying rate had an extreme value point, and the maximum drying rate did not necessarily in the position of hot air inlet and outlet of drying layer. Indeed, the drying rate of counter flow was significantly higher than concurrent flow drying under the same drying conditions of ventilating temperature, humidity and air volume. And in cross flow and standing drying, the drying rate in the position of hot air inlet and outlet had a big difference. When the layer thickness was 0.5 m, and the grain moisture content was more than 20%, the drying rate was nearly zero in the air outlet. This paper pointed out that the change process of grain drying was from initial state point(wet grain)to the final state point (dry grain), the uniformity of cross flow and standing drying was poor, and the counter flow drying technology was more energy-saving than concurrent flow. The experiment was studied in 5HP-3.5 type circulating and tempering dryer, and the results showed that the analytical values and measured values of paddy moisture content in dryer export presented high fitting degree after experiencing the drying and tempering every time. And the maximum deviation between analytical values and measured values was 0.69%, the range of drying process was 0.27%-0.69%. Grain drying was a typical larger inertia and nonlinear process, which pointed out the reason for deviation should be detection error caused by instrument, and confirmed the reliability of the analytical results. The given analytical method avoided the problem of the poor reliability of grain moisture on-line detection instrument and the thin bed superposition simulation error accumulation under the grain drying conditions of high temperature, high humidity and high dust. The analytical methods were of great significance for achieving dynamic tracking and regulating of the grain drying process, guiding drying design, as well as achieving high efficiency and energy saving, improving the drying efficiency and capacity of the dryer.