Abstract: Thermal conductivity coefficient, as one of the important physical parameters of rock, is of great significance in geothermal energy development and geotechnical thermal engineering application. The current test method requires the collected rock samples to be processed in the laboratory. The transportation and processing can damage the rock structure and affect the water content. It needs a complex test process, and yields inaccurate results. This study proposes a new test method to obtain the thermal conductivity coefficient of rock on site. The contact surface between rock surface and probe is filled with thermal coupling agent to reduce thermal contact resistance during the test process, and the field thermal conductivity test is carried out with the aid of the thermophysical property tester. The optimal ratio of thermal coupling agent is determined by the comparison experiment of preparing thermal coupling agents by fully mixing different amounts of thermally conductive silicone grease and copper powder. The experiment shows that the application of thermal coupling agent can effectively reduce the thermal contact resistance between probe and rock surface, and improve the test precision. Moreover, the thermal coupling agent itself has little effect on the thermal conductivity coefficient of rock. The research results can provide reference for obtaining thermal conductivity coefficient of rock accurately and conveniently in the field.