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Qinghai is located in a permafrost region, which belongs to the continental climate zone of the the Qinghai-Tibet Plateau. At the same time, freezing-thawing cycles are common destructive factors for roadbeds and foundations. In order to examine the effects of freezing-thawing cycles on actual projects in Qinghai and reveal the mechanisms of freezing-thawing cycles on damage of the projects, the freezing-thawing cycle test, unconfined compressive strength test and electron microscope scanning test of the undisturbed loess and remolded loess in the Xining area of Qinghai are conducted to analyze the influence of different freezing-thawing temperatures and different freezing-thawing cycles on the strength and microstructure of the undisturbed loess and remolded loess. The results show that when the loess undergoes 0-6 freezing-thawing cycles, the strength of the undisturbed loess and remolded loess gradually decreases. After 8-10 freezing-thawing cycles, the unconfined compressive strength of the loess first increases and then tends to be basically stable. The strength of the undisturbed loess decreases with the decrease of the freezing and thawing temperature. However, the strength of the remolded loess first increases and then decreases with the decrease of temperature. From a microscopic point of view, the decrease in freezing-thawing temperature and the increase in the number of freezing-thawing cycles both lead to the decomposition of large loess particles into small particles, and the arrangement of the particles has changed. The results are of reference value for actual project construction and construction in the Xining area of Qinghai.