A kind of circulated duplex telescope for synthetic-aperture laser imaging radar is presented, in which a circulator connects among a reception-channel 4-f system with defocusing and phase biasing, a transmitting-channel 4-f system with defocusing and phase biasing and a primary telescope. By controlling the biasing functions and the defocusing amounts of both channels it is realized with a single telescope to receive the echo with its aberration eliminated and to transmit a beam with an additional quadratic phase. As a result, a suitable and controllable phase history can be generated to correctly synthesize the image in the azimuth-direction. The designs as well as a full transmission equation are detailed in the paper.