The scalability of system is a puzzle to design high performance computers. NUMA (non_uniform memory architecture) architecture is proposed for scalable system underlying a shared memory pattern. Research and practice results show that the scalability of system tightly correlates with that of the operating system. Usually, two structures of operating system are employed in multiprocessor systems, monolithic based on shared memory and multi kernel based on message passing. However, both of them cannot fully fit scalable parallel computers, especially MPP systems with NUMA architecture. In this paper, the problems in two structures are analyzed, a new structure, multi-virtual-space and multi-mapping with active message, is proposed. The test and practice results show that the new structure is successful in the scalability of system. This paper introduces detailedly the implementation of the structure in a MPP system with NUMA architecture.