Vertical pressure due to self-weight of grain bulk has significant effect on compression and density in large grain storage. The density change will further induce variation of grain properties, such as heat conductivity rate, and finally affect the mildew of grain. By the study, an inexpensive and easy-to-use system was designed to study the effects of vertical pressure on compression and heat production due to mildew. First, the wheat bulk with wet-basis moisture content of 22.2 % was compressed under vertical pressure of 0, 200 and 440 kPa through a one-dimensional oedometer. The compression and creep behaviors were investigated using the strain/settlement ∼ time results. Second, aerobic plate counting (APC) and germination test were performed to study the effect of vertical pressure on the mildew effect and storage quality. Third, a finite element model considering compression induced change of grain properties was established to simulate the temperature variation caused by physical environmental factors and used to back-estimate the temperature rise induced by biological reason, i.e., fungi. Finally, a newly reported solution of biological field was employed to theoretically analyze the heat production due to fungi using the difference of temperature between simulation and test.