The invention relates to a simple, economical and non-toxic insect-killing and preventing new preservation method for existing large granaries, aiming at solving the problems that grains easily go bad and have pests and pesticide residue after being persevered and stored by using high-toxic pesticide and high-temperature oxygen enrichment for a long time. According to the method, oxygen-containing air evacuation and inert gas filling are mainly carried out on the granaries having a sealing condition, so that the aims of anaerobic insect-killing and preservation are achieved; the method is very suitable for state farms and large farmer-households.