Focus tunable lenses are increasingly important in optical applications such as presbyopia correction, VR/AR systems, and medical endoscopy. Conventional liquid crystal (LC) lenses adjust the focal length via refractive index modulation induced by molecular reorientation. However, these systems suffer from polarization dependence, a limited focal tuning range and structural complexity. Here, we develop a focus-tunable lens integrating a silicon lens with vertically aligned liquid crystal elastomers (LCEs). Upon temperature variations, the LCEs reversibly change diameter by up to 80% through an order-to-disorder transition, inducing curvature changes in the lens. As a result, the focal length increases by about 170%, significantly exceeding that of previously reported focus-tunable lenses. This actuation-driven curvature modulation provides a simple yet effective approach for achieving large focal-length tuning, demonstrating the strong potential of LCE-based tunable lenses.