Abstract: A thermal resistance correction factor aimed at the backfill material of the borehole was developed by analyzing the unsteady heat transfer of vertical embedded pipe for ground source heat pump, and the heat shortcircuit modification was introduced to modify the mean temperature of the circulating water. Meanwhile, a cylindrical source integrated modified model was developed based on the modification of the existing Carslaw cylindrical source model. The accuracy of the modified model was proved by the comparison of the calculation result and the experimental one, and the influence of the backfill grout, the equivalent radius, thermal ununiformity and the heat shortcircuit on the result was also further analysed.