Traditional space telescopes can improve the resolution by increasing the system aperture in accordance with the diffraction limit formula of resolution. However, as the corresponding volume and weight of the system are increased, it is difficult to be carried on a spacecraft. The emergence of Negative Index Materials(NIMs) provides a new way for the development of highresolution space telescopes. This paper introduces the history and research of NIMs and outlines their special properties, such as negative group velocity, inverse Doppler effect, abnormal Cerenkov radiation and negative refraction effect, then it discusses the functions of NIMs and why the NIMs can be used to improve the telescope resolution. It points out that NIMs amplify evanescent fields containing information of the fine structure of objects and decaying exponentially in a vacuum with distance, so that the evanescent fields can participate in imaging. These properties of the NIMs make the resolution of an optical system better than the traditional diffraction limit.