Kylin is a server operating system focusing on high performance and security. In this paper, a hierarchical kernel structure for Kylin operating system is proposed. Under this structure, Kylin is organized into two layers. The basic kernel layer is responsible for initializing the hardware and providing basic memory management and task management while the system service layer is based on FreeBSD providing UFS2 file system and BSD network protocols. In terms of this conception, the motivation for this novel hierarchical operating system kernel model is discussed. Then the kernel's infrastructure is introduced. Last, the performance comparison of Kylin, Redhat 9.0 and FreeBSD 5.3 with standard benchmarks is presented. Finally, a discussion of the future directions of Kylin operating system is made.