The invention relates to a method for preparing PC/ PET alloy material, and belongs to plastic shaping processing technology. It comprises: mixing milled PC granulate powder, PET sheet and lubricating agent, precrystallizing, drying, mxing refining, plasticizing, neck ring mold shaping, cooling and calendering. The PC/ PET alloy material is characterized by good thermal resistance, strength, tranparency, good size stability and small thickness deviation, and is ideal replacement for electrical switching membrane, car instrument board and car glass, and the production method is characterized by low cost and high efficiency.