Influences of the thermal diversification to the accuracy of optical element and relatively position of the opto-mechanical system are analyzed. The scale ratio of the optical distance diversification and the defocus error of optical system is derived. Through integrated opto-mechanical design and analysis of image quality of the 1.23 m aperture telescope, an opto-mechanical system (fitting the thermal diversification of －35 ℃～+55 ℃) is built that meets the requirements of imaging of the telescope. It is also validated that the main influence of the thermal diversification to the telescope is defocus error, and some practical compensation methods such as focus mechanism on secondary mirror to satisfy the requirements of observation of the telescope are presented. Meanwhile, some feasible opinions for the observational experiments and upgrading of 1.23 m aperture telescope or larger aperture telescope analogously are proposed.