Steel corrosion is one of the most serious problems for industrial safety. In this paper,steel surface corrosion is detected and evaluated by pulsed eddy current thermography. A two-dimension inductive heating model is built to analyze the influence of corrosion geometry on its surface temperature distribution. Corrosion extent is then characterized by the root mean square of the surface temperature base on experiment data. The effect of coat on the steel corrosion extent is also studied. With principal component analysis method,factor analysis method and pulse phase analysis method,the infrared images of the steel samples are reconstructed to improve the abilities of corrosion recognition and corrosion extent evaluation.