Liquid lens has many advantages such as rapid zoom, low power consumption, low cost, etc, which determines its wide application in UAV, endoscope and other fields. The classification and working principle of liquid lens are introduced, the Gaussian theoretical calculation of liquid lens focusing is carried out, and the relationship formula between the focusing distance and the focal length of liquid lens is derived, too. A 110° objective optical system with liquid lens is designed, and the detector of the system is a 1/4 inch CMOS chip, and aberration of the optical system can meet the application requirements. Finally, experimental verification has been conducted on the physical object of this system and the results successfully meet the established design indices, as well as specified requirements for utilization in micro-lens applications.