Abstract: Vibrothermography (VT) is a rapidly developing version of InfraRed (IR) thermographic Non-destructive Testing (NDT). VT can be applied to the detection of internal flaws in materials, and holds a great promise for detecting cracks in alloy material and composite structures used in aerospace industry. In order to reveal the physical mechanism and influence factors of VT, which provides theoretical guidance for the design of test conditions of VT, a numerical simulation of the process of VT is conducted by the ANSYS finite element method. Taking a crack in an aluminum alloy beam as the detected object, the vibration-heat transformation mechanism of the crack, and the relations between the transient temperature and testing conditions are analyzed. The effects of the thickness of the specimen, opening width of the crack, holding pressure and exciting force on the temperature increase at the crack are calculated and discussed respectively. The results show that the temperature increase at the crack faces closed to the crack tip has a significant change which is shown as a wave type rising in the time domain. It is proven that the friction and thermos-elastic effect are the reasons for the temperature rise of the crack defects of aluminum alloy beams. Friction is the main reason.