We report a two-layer model to describe the thermal response of continuous-wave (CW) terahertz (THz) irradiated skin. Based on the Pennes bio-heat conduction equation, the finite element method (FEM) is utilized to calculate the temperature distribution. The THz wave with a Gaussian beam profile is used to simulate the photo-thermal mechanism. The simulation results show the dynamic process of temperature increasing with irradiation time and possible thermal damage. The factors which can affect temperature distribution, such as beam radius, incident power and THz frequency, are investigated. With a beam radius of 0.5 mm, the highest temperature increase is 3.7 K/mW.