Based on the theory of line-heat-resource，the soil comprehensive thermal conductivity coefficient and heat transfer rate of u-tube ground heat exchanger are tested and calculated in Zheng-ding of Shijiazhuang aera with the constraint optimization method and using the soil thermal physical instrument produced by the Hebei University of Engineering. According to the experiment results, the impact factors of time step，average temperature of inlet outlet u-tube ground heat exchanger and heating power on the heat transfer rate of u-tube ground heat exchanger were discussed. The results show that the comprehensive thermal conductivity of the soil tends to be stable after 20 hours; the comprehensive thermal conductivity of the soil the average temperature of inlet and outlet u-tube ground heat exchanger, and the heating power could influence the heat transfer rate of u- tube ground heat exchanger, and the influence would reduce successively.