The paper presents the results of numerical simulation of thermal response test (TRT) and the results of the experiment of TRT in Johan Paul the second Centre “Have No Fear!” in Cracow. The aim of the study is to determine and compare the values of effective thermal conductivity of rocks obtained in TRT experiment with the results obtained from the numerical simulation of TRT. The results are shown as graphs of temperature variation in the time on inlet and outlet of the borehole heat exchanger (BHE) and as drawings of thermal distribution. Borehole heat exchanger is constructed of a single u-tube at a depth of 180 m. In the numerical simulation of TRT was included geological profile of the rock mass and the associated changes in thermal properties of rocks. Temperature dependence of liquid viscosity were also adopted. Groundwater flow has been neglected. Presented mathematical model based on energy balance equation, Navier-Stokes equation and flow continuity equation was solved using the finite volume method. To numerical calculation was used ANSYS CFX software.