The thermal conductivity of calcareous sand affects the heat transfer process of the surrounding soil and causes the change of engineering mechanical properties and disaster effects of calcareous sand at different ambient temperatures. The variation law of thermal conductivity of cemented calcareous sand with five different cement contents (P_s=5%, 7.5%, 10%, 12.5%, 15%) was analyzed based on hot needle method. SEM, MIP and NMR were used to comprehensively reveal the essential characteristics of micro-pore structure changes of cemented calcareous sand during the process above. On this basis, the microcosmic mechanism of the evolution of the thermal characteristics above was explained. The results show that the thermal conductivity (λ) of cemented calcareous sand increases with the increase of cement content (P_s). When P_s is less than 10%, λ increases linearly, and when P_s is more than 10%, λ increases slowly. With the increase of cement content (P_s), the number of pores in the cemented calcareous sand becomes less, and the proportion of pores decreases obviously. However, when P_s increases up to 10%, the change of micro-pore structure parameters such as total pore area, pore number and porosity stabilizes. The thermal conductivity (λ) of cemented calcareous sand with different cement contents is negatively correlated with the changes of their microscopic pore structure. The reason lies in that the gel-like cement hydration products continuously fill the pores of cemented calcareous sand, reducing its porosity and improving the heat transfer inside the sand sample. The macroscopic performance is that its thermal conductivity (λ) increases with the increase of cement content (P_s).