Abstract: Coming into 21 century, a number of developed countries and relational government organizations in the world, such as National Aeronautics and Space Administration(NASA) in America, European Space Agency (ESA), and some organization in Russia, have established a series of strategic projects about space science development. These projects point out some problems to be solved in space science and provide the way forward for space technology, also it indicate that development of space science is dependent on advance optical and radio telescope as well as their instruments. Therefore, this paper introduces some large astronomical telescopes used in international space science studies at the beginning of 21 century, and describes several optical systems in large aperture space telescopes mainly. Finally, the wave front sensing technique which is the key technology in the development of large astronomical telescopes is discussed.