Abstract: In eddy current pulsed thermography, the short-high-frequency current excitation is applied to the test piece. The crack surface generates instantaneous heat due to the accumulation of the eddy current, and then the temperature distribution of the specimen is caused by heat conduction. In this paper, the current distribution model and simplified heat transfer model were established to explore the characteristics of the surface temperature distribution of the specimen. Furthermore, a series of penetrating fatigue cracked metal specimens with different lengths were made, and the relationship between the thermal response and the crack length was studied. The numerical simulation and experimental results show that the thermal response of the crack region is linear with the crack length under certain detection conditions, and satisfying the positive correlation, which prove the correctness of the simplified heat transfer model. The research results enriched the heat transfer theory of ECPT, which laid a theoretical foundation for the engineering practice of the technology.