The invention discloses a PBT molding composite and a preparation method thereof. The composite of the invention comprises the following components by weight percent: 10-60% of PBT, 10-50% of packing reinforcer, 0-35% of composite fire retardant, 0.1-5% of cyclic polymer and 0.1-4% of additive. The invention also provides the preparation method of the PBT molding composite, comprises the following specific steps: weighting each component with a measuring balance according to the percentage, mixing the components at 200-300 DEG C with a twin-screw extruder, discharging wire-shape material, cooling and pelleting. The PBT molding composite of the invention can greatly increase the flow property of the material and the method of the invention is simple to operate, is easy to control and is convenient for industrialized production.