To analyze properties of frozen ground and bearing capacity of tower foundation for the Qinghai-Tibet DC Engineering， tests of fine-grained soil properties and frustum-column spread foundation loading under three-directions loading condition were carried out in the Wudaoliang area of Qinghai-Tibet Plateau， while the shallow backfilled ground was in the freezing and thawing state. According to results of loading tests， bearing characteristics of frozen ground and tower foundation was analyzed， and ultimate bearing capacity was obtained in the interaction limit state between foundation and ground through establishment and fitting analysis of the load- displacement hyperbolic model. Based on measured values of soil tests， engineering properties of the ground were studied， the ground surface settlement of thawing period relative to freezing period was calculated and was 0.23m， and the calculated value was consistent with actual situation. For thawing or freezing state of seasonally thawed layer， the stability analysis model and method of tower spread foundation under uplift conditions were proposed respectively， and uplift angle of frozen backfilled soil was calculated and was 20.5°. The results show that shear strength of ground and bearing performance of foundation are larger in the freezing state than in the thawing state of seasonally thawed layer， and the bearing capacities of foundations can meet the design requirements. Void ratio of fine-grained soil is reduced， density is improved， water content and degree of saturation are increased while frozen soil thawing. The freezing or thawing state of soil has great influence on mechanical parameters of ground including the shear strength， uplift angle， etc. So keeping the freezing state of deep backfilled ground is very important to bearing safety of the engineering foundations.