The focusing and leveling sensor is one of the key subsystems in lithography system. It is used to measure the height map of silicon wafers before exposure. The projection optics is the most important module of the focusing and leveling sensor, its' imaging quality directly affect the measurement accuracy of the sensor. According to the measurement principle of the sensor and aberration theory, the influence of magnification, distortion, tele-centricity, and resolution on the measurement accuracy of focusing and leveling sensor is analyzed. A reflective optical design is chosen for the projection optics, which has characteristics of simple structure, no chromatic, and small distortion. After the optimization and tolerance analysis by using Zemax software, the working wavelength of designed system is 600-1000 nm, root-mean-square radius of the diffuse spot is less than 0.189 μm within a field of view of 3 mm×26 mm, its magnification is 1.000, maximum distortion is 0.0008%, modulation transfer function is 0.74@33 lp/mm, and tele-centricity is 0.04 mrad. The results show that the reflective optical design for lithographic focusing and leveling sensor is engineering feasible with the current opto-mechanical manufacturing and assembling capability.