The thermal conductivity of calcareous sand affects the heat transfer process of the surrounding soil , causing the change of engineering mechanical properties and disaster effects of calcareous sand at different ambient temperatures. The thermal conductivity of cemented calcareous sand with five different cement contents (Ps=5%, 7.5%, 10%, 12.5%, 15%) was analyzed based on hot needle method. By means of SEM, MIP and NMR, the essential characteristics of micro-pore structure change of cemented calcareous sand during the above process were revealed. On this basis, the microcosmic mechanism of the evolution of the above thermal characteristics was explained. The results show that: (1)The thermal conductivity of cemented calcareous sand λ increases with the increase of cement content Ps. When Ps is less than 10%, λ increases linearly, and when Ps is more than 10%, λ increases slowly. (2) With the increase of cement content Ps, the number of pores in the cemented calcareous sand becomes less and less, and the proportion of pores decreases obviously. However, when Ps increases to 10%, the change of micro- pore structure parameters such as total pore area, pore number and porosity slows down. (3)The thermal conductivity λ of cemented calcareous sand with different cement content is negatively correlated with the changes of their microscopic pore structure. The essential reason is 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 Ps.