The invention relates to a formula of a glass fiber-impregnated PA6 (nylon 6) with high weather-resistant property and high fluidity and a preparation method thereof. The formula comprises the following components in parts by mass: 100 parts of PA6 resin (1), 0.5 to 1.6 parts of anti-ultraviolet aging additive (2), 0.5 to 1 part of antioxidant (3), 0.2 to 1.2 parts of flowing promoter (4), 2 to 10 parts of toughener (5), and 1 to 5 parts of compatilizer (6). The preparation method comprises the following steps of premixing the components according to a certain ratio; using a double/single-screw extruder to melt, mix and extrude into a die head, separating flow and impregnating, so as to obtain the glass fiber-impregnated PA6 with high weather-resistant property and high fluidity. The formula and the preparation method have the advantage that by combining hyperbranched end active functional groups and glass fiber, the interface bonding ability between polyolefin resin and glass fiber is enhanced, and the mechanical property is improved.