An aspherical zoom optical system is designed to solve the problems of adjustment of internal and external coherence factors, lack of energy utilization and short life of module of NA 1.35 immersion lithography system. This zoom optical system consists of both three lenses groups and the stop as well as the image plane. The system consists of 7 pieces of lenses with pupil diameter of 42 mm, view angle of 1.89°, which can realize the focal length of 700 mm~1 830 mm, zoom ratio of 2.16, and the three aspheric surfaces are all designed in concave surfaces of optical elements. The design results show that the system is with good imaging quality of RMS diameter less than 40 μm and distortion less than 0.5%, which can satisfy the usability requirements of the immersion lithography lighting system.