Abstract: The thermal conductivity (TC) of the sand, clay and rock is measured by QTM-D2. And the effects of different experiment sizes and different conditions of saturated samples are discussed. The size error of TC among different samples is found out through experimental results and numerical simulation, which offers a solution to the measurement of TC of the geotechnical materials in site. During the measurement of TC by use of the heat line, the effect of sample size is limited, and the measured results of samples with different geometric sizes are similar. According to the domestic and international studies on empirical relation between TC and temperature, the empirical relation between the temperature and TC at the condition of normal temperature is obtained, and the thermal variance coefficient β is also obtained, based on a large number of measured data and numerical calculations. The values of β of geotechnical materials are small, mostly with magnitude 10-3, and the curves of TC and temperature is approximately linear. These coefficients and the experimental relationships are important to the understanding on the TC of the geotechnical materials in north China and to the temperature simulation programming as well.