According to the requirements of corona detection on searching targets with large field of view and detecting objects with small field of view, a refractive zoom optical system using mechanical compensation technology and working at“solar blind”ultraviolet wavelength (0.24~0.28 μm ) is designed. According to the requirements of users, the focal length spreads from 30 mm to 60 mm, and F number is 3.5. PIXIS 1024BUV CCD with size of 1 inch (1 inch=2.54 cm) and pixel size of 13 μm ×13 μm is used as a sensor. The field of view of the system is 8°~16°. The zoom lens consists of eight lenses with two aspherical surfaces, so it has the advantages of low cost and simple structure . The design results show that the modulation transfer function (MTF) of the zoom system is higher than 0.7 at cut off frequency of 38 lp/mm. The optical performance at all fields of view and all zooming conditions is close to the diffraction- limited image, and the distortion is less than 3% . So the zoom optical system presents a good image quality, and can meet users′ requirements.