The invention relates to the technical field of polymer material, belonging to a transparent PC/PET composite material and a preparation method thereof. The composite material is prepared by the components with the mass percent: 70-90% of polycarbonate (PC), 10-30% of polyethylene glycol terephthalate (PET), 0-0.5% of compatibilizer, 0.1-0.3% of transparent agent and 0-0.5% of antioxidant. The transmittance of light of the material is more than 80%, the cantilever girder notch impact strength is 10-55KJ/m<2> under the condition of below 23 DEG C, the bending modulus is 2100-2400MPa, the melt index is 10-30g/10min under the conditions of 260 DEG C and 5Kg, and 0.45MPa heat deflection temperature is more than 130 DEG C. The transparent PC/PET composite material has the characteristics of high grade of transparency and mechanical property as well as good heat resisting property and dimension stability; under the premise of ensuring the PC transparency and the mechanical property, the invention improves the oil resistance, solvent resistance, wearability, stress cracking resistance and processing fluidity of the PC, and can be widely applied to the fields such as household electrical appliances, electronic apparatus, building materials, automobile, etc.