According to the requests of the customers, the optical parameters of the objective on small UAV are calculated at first, and the optical design characteristics of the objective are obtained. And then based on the characteristics, a small refractive objective with 52.5 mm focal length, F/2 relative aperture, 12° field of view and 286 lp/mm Nyquist frequency at visible light waveband on UAV is designed. CMOS devices with 1.75 μm single pixel are chosen as receiving devices and small aberration complementary conception is adopted to reduce the tolerance sensitivity of the optical system. Finally, the tolerance analysis is performed to the design result. The results of tolerance analysis show that optical design characteristic requirement can be better met.