Because of the increasing energy need in China, a lot of deep and complex reservoirs are to be exploited with more and more complex problems in drilling. The narrow safety density window of drilling fluid is one of the most prominent problems. MPD technology is the best way to solve this problem currently, which can be divided into constant bottom hole pressure system and micro-flux control system. By the analysis on these two basic styles of processes and equipments, the difference between these two systems is compared in order to provide recommendations for the further promotion of MPD technology.