The in-situ testing instrument for ground thermophysical properties can be used to measure accurately the ground thermophysical parameters. This paper describes the in-situ testing instrument in terms of its principle, structure and components, characteristics， testing method and data processing. With the Ingersoll simplified model， it is found that a total of 498 geothermal wells with depth of 100m are needed to meet the heating requirement in Shuangliao Service Station.