There were many harmful gases in the process of storing grain in large granaries, which can not only cause environmental pollutions, but also endanger people's health. Reducing harmful gases in granaries and ensuring grain quality had become the focus of food storage industry. In this paper, the sources, types and harms of harmful gases produced in the process of grain storage were briefly described, and the relative degradation methods, principles, advantages and disadvantages of phosphine, were also introduced in detail. Furthermore, the feasibility of degradation of harmful gases in granary by plasma technology was emphasized, and the problems to be solved in practical application of this technology were raised.