For ± 800 kV UHV DC transmission line construction in cold regions, it is necessary to solve the design problem of low temperature brittle fracture, in order to prevent the brittle fracture of steel structure members under low temperature without reaching the yield stress. Taking ±800 kV Hami-Zhengzhou DC transmission line as the study object, this paper introduced the mechanical properties and principles of tower components under low-temperature environment, based on the theory and test results of brittle fracture under low temperature at home and abroad. Combined with practical engineering, a strength design method was proposed and the design parameters were studied in detail for steel structure members under low-temperature environment. At last, some reasonable reduction factors were recommended. The results presented in this paper could be used as references for the design of DC transmission tower.