The invention discloses a low-temperature type flame retardant epoxy resin adhesive and a preparation method thereof. The preparation method comprises the following steps of mixing epoxy resin, epoxy resin thinner, defoaming agent, and toughener, and uniformly stirring, so as to obtain a component A; mixing phenolic modified amine, accelerant and coupler, and uniformly stirring, so as to obtain a component B; finally, uniformly mixing the raw materials of component A and component B, so as to obtain the low-temperature type flame retardant epoxy resin adhesive. The low-temperature type flame retardant epoxy resin adhesive has the advantages that the phenolic hydroxyl, thiocarbonyl and secondary amino group type low-temperature active groups and the phosphorus-nitrogen synergistic flame retardant elements are contained, so that the low-temperature experiment and halogen-free flame retardant effects are realized; the construction is convenient, the odor is little, the applicable period is long, the heat discharging is stable, the flame retardant property is excellent, the low-temperature and quick-curing effects are realized, the adhering with a substrate is good, and the impact-resistant property is realized; the problems of difficulty in curing and failure to self flame retardancy at low temperature in the existing epoxy resin adhesive are solved, the preparation method is simple, and the control and industrialization are easy.