Average thermal parameters of the whole heat exchanger can be measured by in situ thermal response test (TRT). TRT can simulate the actual operation of the ground source heat pump (GSHP) and has been widely used in designing the GSHP. Data of TRTs from 89 different boreholes in China were collected and analyzed. Effective thermal conductivity (λeff) of the ground within 200 m was analyzed and its influencing factors were evaluated. Results show that thermal conductivity from TRT results are mostly between 1. 50 and 2. 16 W/(m·K) with cumulative probability between 25%~75%. Generally speaking, underground materials with coarse grain, high water yield and strong groundwater velocity show better heat transfer capacity. Lithology, water content and groundwater flow are import influencing factors for effective thermal conductivity. The regional variability of the underground material and groundwater level depth within 200m are important factors controlling effective thermal conductivity. Groundwater flow also plays an important role and the modified Peclet number (Pe) is introduced to define the effect of groundwater flow. When Pe is between 0. 28 and 0. 84, a 47% increase in Pe number results in a 7. 56% increase in the effective thermal conductivity of the ground.