Abstract: Microkernel operating system appeared in recent years, and has become the trend of operating system development. Microkernel operating system has many advantages. But one serious problem existing in most of the nowaday microkernel operating systems is that the performance is not good. The things leading to the worse performance of microkernel operating system are the bad kernel structure and the structure of the whole operating system, as well as the improper technologies used in the construction of microkernel operating systems. Also analyzed are the factors lying in the structure of microkernel operating system that affect the performance, and how they act on the performance. These factors are the things that must be dealt with carefully in the research work of microkernel operating systems.