The invention relates to a glass fiber reinforced and hydrolysis-resistant nylon PA (Polyethylene) 6 / PA66 composite material and a preparation method thereof. The composite material comprises the following components: PA6, PA66, hydrolysis-resistant alkali-free glass fibers, a compatilizer, a main hydrolysis resisting agent, an epoxide assistant hydrolysis resisting agent, a nucleating agent, an antioxidant that is the 1010 and 168 compounded antioxidant, a lubricant and simethicone. The preparation method comprises the following steps: placing the PA6, the PA66, the compatilizer and the simethicone into a high-speed mixer to mix according to the formula mass; adding each assistant mentioned above; mixing by the high-speed mixer; transferring into a twin-screen extruder; and molting, extruding, blanking and drying the materials, so as to obtain the composite material. The glass fiber reinforced and hydrolysis-resistant nylon PA6 / PA66 composite material has the advantages of being high in bending strength, excellent in toughness and hydrolysis resistance and wide in applicable scope, is mainly applicable to components of controllers of electric bicycle, and can meet the requirement of the performance of the materials.