Abstract: The researches on heat conduction characteristics of soft soil under high temperature are performed for further determining the load change on tunnel lining structure surrounded by saturated soft soil and accurately evaluating its safety under high temperature of fire. The experiment adopts the method of thermal needle probe procedure, proposed by American Society for Testing and Materials (ASTM) as the standard method for determination of thermal conductivity of soil and soft rock, by using self-made apparatus for coefficient of thermal conductivity of soil to measure the coefficient of thermal conductivity of Shanghai mucky clay under high temperature. The thermal conductivity of soil samples with different water contents is measured respectively under different temperatures. At the same time, as calibrating instrument, the KD2 thermal conductivity measuring apparatus is used to calibrate the test results. The test results indicate that the thermal conductivity of soil with the same water content increases with the increase of temperatures. When the temperature is low, the increase rate of thermal conductivity of soil is higher, and when the temperature is high, the increase rate of thermal conductivity of soil is lower, which is more serious due to the decomposition of the organic soil under high temperatures. Further, the thermal conductivity of soil with the same temperature increases with the increase of water content.