The dielectric elastomer has the characteristics of compact structure, large deformation, fast response speed, and easy integration. In order to reduce the driving voltage, the dielectric elastomer is applied to the liquid lens and the separation structure of dielectric elastomer and the lens membrane are used. Mathematical models of elastic body active membrane deformation, lens membrane deformation and focal length of liquid lens are established. Simulation results show that when the initial liquid pressure is 500 Pa and the driving voltage is 1000 V, the zoom range of the liquid lens is 15.13--22.80 mm, and the focal length increase is 51%. The effects of the Young's modulus, residual stress, initial thickness and radius of the dielectric elastomer on the focal length of the liquid lens are analyzed. The results show that the initial thickness of the dielectric elastomer has the greatest influence on the focal length of the liquid lens at the same increase in magnification, followed by the residual stress, the research results can provide a reference for the optimal design of liquid lens driven by dielectric elastomer.