High-temperature resistant adhesive film and a preparing method thereof are disclosed. High-temperature resistant thermosetting resin and a flexibilizer are mixed, micro-nano chopped fibers and a heat-liable oligomer are added into the mixture and fully mixed in a solvent, and the adhesive film having a certain thickness is prepared by adopting a solution process. Based on a design of double functions, namely adhesion and thermal stress buffering, the adhesive film can achieve in-situ foaming at a high curing temperature on the one hand, and on the other hand the adhesive film has high toughness so that composite materials and metal structures can be adhered well, peeling strength can be improved and potential corrosion can be avoided.