Abstract: The commonly used method of power battery capacity detection of electric vehicle neglects the characteristic of chemical reaction with charge transfer which occurs in the process of charging and discharging of the battery, so it is difficult to detect the power battery capacity and its fading accurately and nondestructively. We proposed the tomography image detecting method of the capacity fading of power battery. The detection technique of tomography image and the commonly electrochemical performance detection technique were integrated. The experiment system of power battery capacity fading was established. The object of the research was the capacity fading of LiFePO4 power battery which used in pure electric vehicle usually. The relationship between the electric performance parameters of power battery and its structure morphological parameters was studied based on the principle of battery electrochemical and computer tomography. The experimental result shows that the tomography image method is practical, correct and non-destructively.