When the bias voltage is low,PEM (Photon Emission Microscopy) failure signal is weak and is easy tobe influenced by noise,which results in a poor quality of PEM image.In order to solve this problem,a signal- noisemodel of PEM image is established,and a differential image localization algorithm is designed to improve the PEMprecision.First,this algorithm acquires two groups of images with different failure signal strengths by adjusting thebias voltage.Then,the average differential image of these two group images is calculated and dealt with by meansof mean filter and image binarization,thus obtaining a statistical image.Finally,IC failure points can be effectivelylocated according to the statistical image.Physical analysis demonstrates the accuracy of IC PEM based on the pro-posed differential image localization algorithm.