Abstract: In this paper, the PRESENT algorithm is analyzed by the improved electromagnetic attack. The sensitive areas are found through magnetic coil over cipher chip on physical experiment platform. Differential electromagnetic analysis is implemented on the output of S-box and that of XOR. The results of analysis are mutually supported and complemented. In this way, 64 bits of the 80 bit original key can be recovered efficiently. The other 16 bits can be recovered through exhaustive attack and then the 80-bit original key could be recovered. In the analysis process, the peak value of the difference between mean values leaks the information of sub-key operating order in cipher chip. Furthermore, a flaw in the original PRESENT algorithm description is pointed out and corrected.