The invention discloses a long glass fiber enhanced nylon PA66 composite material resistant to creep deformation in a high temperature oily environment and a preparation method thereof. The compositematerial mainly comprises following components in percentage by weight: 40 to 50% of long glass fiber, 48 to 55% of low viscosity modified nylon PA66, and 0.5 to 5% of antioxidant aid. The preparationmethod comprises following steps: extruding commercial PA66 resin by a double screw extruder, and evenly dipping the surface of long glass fibers in molten PA66 resin, namely, an impregnation preparation technology is used for preparing the long glass fiber enhanced nylon PA66 composite material. The preparation method has the advantages that proper raw materials are selected and modified to obtain PA66 with low melt viscosity; a large volume product can be rapidly moulded, the moulding period is shortened, and at the same time, a certain amount of modifier is added to enhance the anticorrosion and creep deformation resistant performance in a high temperature oily environment.