The invention discloses a light-weight fiber-reinforced phenolic sandwich plate and a preparation method thereof. The light-weight fiber-reinforced phenolic sandwich plate is composed of two surface layers and a core material layer between the two surface layers or is composed of two sandwich surface layers and a core material layer between the two sandwich surface layers, and the core material layer is a fiber-reinforced phenolic light-weight foam layer. The plate disclosed by the invention solves the problem of brittleness of phenolic foam, and the plate is composed of phenolic materials with better flame resistance from inside to outside, so that the flame resistance of the plate is excellent, the plate can resist to high temperature of 150-180 DEG C, the plate strength retention ratio at high temperature is high, and thus fireproof requirements of locomotives can be met. The core material and surface layers of the plate are light materials, so that the light-weight requirement of vehicles can be met. The core material and surface layers of the plate are reinforced by fiber, the fiber in the core material can effectively increase the strength and rigidity of the phenolic foam, and the fiber in the surface layers can effectively increase the strength and rigidity of the phenolic plate, so that the obtained sandwich plate has better strength and rigidity.