Abstract: A zoom projection lens is designed to meet the requirements of different sizes of big rear-projection screen with the same light engine and screen location. Since the optical system to be designed should have a big relative aperture, middle field of view and small zoom ratio, the concept of zoom system is selected. The positive mechanical compensation configuration was adopted, the proper magnifications of the zoom configuration were chosen and the Gauss roots were derived. The appropriate primal configurations based on each subassembly are chosen. The optimization design is carried out with ZEMAX optical design software. The distortion of the zoom system is improved, and the modulation transfer function (MTF) is used to evaluate the system. The design and assessment results indicate that the optical performance and image quality of the zoom projection lens system meet the design specification, and can be used in big screen TV, ranging from 101.6cm to 177.8cm.