The invention discloses a glass fiber reinforced styrene/maleic anhydride composite and a preparation method thereof. The glass fiber reinforced styrene/maleic anhydride composite is characterized by being prepared from the following raw materials by weight percentages: 46-90 percent of SMA, 0-2 percent of heat stabilizer, 0-2 percent of processing agent and 10-50 percent of chopped flat glass fiber. The preparation method comprises the following steps that the SMA, the heat stabilizer and the processing agent are proportionally added into a double-screw extruder to be molten, mixed and dispersed, meanwhile, the chopped flat glass fiber is fed into the double-screw extruder from a side feeding mouth to be extruded and pelletized, and the product is obtained. The composite has the advantages of high stiffness, high heat resistance, high size stabilizer, good aging resistance and low smell and meets the requirements of vehicle air conditioners as follows: high stiffness, heat resistance, aging resistance size stabilizer and low smell, and the high performance of the vehicle air conditioner material is realized.