The invention relates to a method for preparing continuous glass fiber reinforced styrene-acrylonitrile copolymers. Styrene-acrylonitrile is taken as matrix component, and continuous glass fibers and polyester resin are taken as reinforcing components. The method includes the following steps: 1) the components besides glass fibers are weighed out according to the weight percents correspondingly; 2) the components are placed in a high-speed mixer, mixed evenly under room temperature and fed into a double screw extruder; 3) the continuous glass fibers are added into the fourth temperature area of the extruder; 4) the components are extruded out, cooled, dried and cut into granules to achieve the desired product. The invention has the advantages that continuous glass fibers are taken as reinforcing component, styrene-acrylonitrile copolymers are introduced into polyester component to enhance the strength and toughness of the copolymers, the blend prepared by the method has relatively high tensile strength, bending modulus and impact strength.