The invention provides a composite high-strength plastic template and a preparation method thereof. The template comprises an upper side plate, a middle plate and a lower side plate, wherein the upperside plate, the middle plate and the lower side plate are arranged in parallel, a plurality of first support members extending along a first direction are arranged between the upper side plate and the middle plate, and are mutually connected on the cross sections perpendicular to the first direction to form a W shape, and a plurality of second support members extending along a second direction are arranged between the lower side plate and the middle plate, and are mutually connected on the cross sections perpendicular to the second direction to form a W shape. According to the present invention, the template has advantages of low cost, high strength and small pore between the plates, such that impurities difficultly enter the pore during the construction so as to ensure the construction quality.