Compared with the traditional mechanical zoom lens, the variable-focus liquid lens has a smaller lens, faster response time, lower cost and higher integration capabilities. These lenses are widely used in image acquisition, target tracking and feature recognition. The performance and applications of liquid lenses are determined by the focal length adjustment method. This paper summarizes the progress of liquid crystals, dielectrophoresis, electrochemistry, electrowetting principle-based function control variable-focus lenses, electrostatic force, electromagnetic force, pressure regulation, and environmental-response-technology-based mechanical driven variable-focus lenses. The integrated applications of variable-focus liquid lenses in optofluidic chips are introduced. Also, the major obstacles and the settlement are described. Furthermore, the development potential and future research direction of the variable-focus liquid lens are also predicted and summarized.