The Hα and White Telescope(HWT) is one of the payloads of the Chinese Space Solar Telescope(SST).To study the impact of the thermal environment on the optical performance of the HWT,the temperature conditions of the thermo-optical testing are designed on the basis of the measurement and numerical simulation of the ground observing condition.A thermo-optical testing system is established to test the optical performance of the HWT under a thermal vacuum condition.The thermo-optical testing system comprises mainly four sub-systems: an optical system to be tested,a vacuum system,a temperature measurement and control system,and a wavefront sensing system.The optical performance of the five important structures in the HWT system at the different temperature conditions is investigated,including the wedges,secondary mirror,primary mirror,collimation lens,and the imaging lens.The results show that when the temperature of the secondary mirror is lower than 40 ℃,the optical performance of HWT is about λ/8,which satisfies the requirement of λ/6.This paper implements a thermo-optical testing procedure for the HWT under different temperature control conditions.The design ideas and test methods are also applicable in similar optical telescope designs for the solar observation.