Variable focus lens based on ionic liquids is investigated by using electrowetting. The presented results show that focusing voltages are strongly affected with reflective index, i.e. driving voltage to obtain identical focal length is remarkably increased with increasing reflective index. The focusing voltage of the lens (<80 V) is quite lower than that of the saline lens (>100 V). Moreover, the lens exhibits excellent performance over saline lens such as good tolerance of sharply temperature varying, wide operating temperature which is up to 80 oC and in particular high stability at high temperature. The adjustable range of focal length varies from 5 cm to the infinite with energy consumption several tenths of a milliwatt low. Besides, it could have potential application in near-infrared image system.