Abstract: In order to achieve a large field of view for a 1.23m large telescope, a near-IR telescope was designed and assembled in this paper. Firstly, an on-axis reflected system was designed based on the optical theory. Secondly, by designing and analyzing the deformation of different support structures for the secondary mirror and the deformation of cylinder type and truss structure, the three-beam secondary mirror support structure and the truss structure were chosen. Finally, the assembly and adjustment was done by a proper secondary mirror adjusting structure and a proper CCD counter-rail. A test was done after the assembly and adjustment, with the result of RMS=0.106 18, PV=0.553 62(=632 nm). It is proved that the design of the near-IR system meets the requirements of the optical design and imaging according to the test result.