Abstract: The YNST (Yunnan one-meter Solar Telescope) auto-guiding system can not only obtain a solar image for guiding but also be used for correcting the primary optical axis of the YNST.This paper describes the optical requirements,mechanical design,and the passive-athermalization technique for the guiding telescope.We analyze the thermal deformation of the guiding telescope caused by solar radiation,and calculate its maximum deflection.The results show that the athermalization design is effective,and the guiding telescope is stiff enough to meet the requirements.