The invention relates to an alloy resin composition and a preparation method thereof. The composition comprises the following components in part by weight: 30-60 parts of polyamide resins, 15-50 parts of ASA (Acetylsalicylic Acid) rubber powder, 10-20 parts of ASA-g-GMA (Glycidyl Methacrylate) resins, 5-15 parts of glossy modifiers, 0-30 parts of AS (Arsenic) resins, 1-8 parts of compatilizers, 5-10 parts of weather-resistant master batch, 1-5 parts of nano fillers and 0.05-0.5 part of antioxidant. The preparation method comprises the following steps of: adding the mixture of all raw materials expect for the weather-resistant master batch to a main charging hole of a double-screw extruder, adding the weather-resistant master batch from a side charging hole, and then carrying out extrusion and pelleting to obtain the product. The alloy resin composition obtained in the method has a softer leopard surface matting effect, a more glossy shiny side lighting effect and better low temperature impact resistance and weather resistance, and is especially suitable for automobile interiors and exteriors with high requirements, such as instrument frames, air outlets of air conditioners, storage boxes, doorknobs, cosmetic mirrors, heat-radiating gratings, rearview mirrors, middle post plates, license plates and the like above wasitlines.