In order to obtain higher angular resolution, the aperture of the space optical telescope is getting larger and larger, and the space telescope with aperture of more than four meters will be difficult to break through the limitation of the effective envelope of the fairing of the existing launch vehicle. On the other hand, the micro-nano optical remote sensing satellite, which has great advantages in terms of development cycle and cost, also has extensive requirements for improving spatial resolution and light gathering area, requiring a smaller launch volume to accommodate a large opto-mechanical system to reduce the launch cost. Deployable space telescopes will be a feasible solution to overcome the limitations of launch size. The research status of deployable space telescopes was reviewed from the aspects of large aperture space astronomical telescopes, segmented mirror deployable telescopes for earth observation and micro-nano satellite optical telescopes deploying along optical axis. Some key technologies and development trends involved in deployable space telescopes were described and summarized.