Grain is a poor conductor of heat. During grain storage, heat transfer in grain pile is a slow process. Therefore, grain temperature in the grain boundary and surface layer is obviously higher than grain temperature that in internal. That is the so-called "hot skin cold heart". The use of external cooling source or the grain heap most cold heart as cold source, the air flow in the granary to reduce the local high temperature storage, thereby reducing or eliminating the temperature gradient in bulk grain, the grain temperature convergence process is called equilibrium grain temperature, referred to as the mean temperature, the method including circulation ventilation temperature technology, local temperature ventilation technology and the use of uniform temperature type grain cooling machine ventilation technology.