Space telescopes are widely used nowadays with the development of space optics and manufacture technologies. Large aperture of telescope means better resolution and observation. However, due to the carrying capacity and outline dimension of rocket, the aperture of telescope cannot be too large. In order to get the large telescope, more and more scientists and engineers are coming to a new idea that assembling the large space telescope on orbit. First of all, the paper makes an introduction about the concepts and types of on-orbit assembly for telescope. Then paper presents some projects which are being conducted and takes one project as an example to introduce specific implementation methods of on-orbit assembly. What's more, high precision robots are needed in this process. Therefore, paper also introduces technologies about the robots for space assembly. At last, the paper summarizes the features and technical difficulties in on-orbit assembly of large space telescope. Furthermore, the paper points out the development directions about on-orbit assembly telescope in the future, which can give some help or guidance to engineers. © 2019 SPIE.