A set of metallic specimens containing fatigue cracks with different sizes were tested using eddy current pulsed thermography(ECPT),therefore the relations between heating response of the crack area and the crack length was studied.The numerical and experimental results both showed that the increase of the crack length enhanced the crack heating response under specific test conditions.A particular form of calculated response signal,which is linearly related to the crack length,was introduced to provide a quantitative evaluation of crack length. A set of metallic specimens containing fatigue cracks with different sizes were tested using eddy current pulsed thermography (ECPT), therefore the relations between heating response of the crack area and the crack length were studied. Numerical and experimental results showing both the increase of the crack length enhanced the crack heating response under specific test conditions. A particular form of calculated response signal, which is linearly related to the crack length, was introduced to provide a quantitative evaluation of crack length.