With the increasing demand of high I/O throughput, highly parallel data transfer and highly scalable storage system, especially in the supercomputing field, the traditional storage system has been difficult to meet the requirements. OBS (object-based storage) system is a new network storage architecture. In OBS system, local storage space allocation is managed by intelligent OSD(object-based storage device), and at present, the OSD is mainly managed by the common file system. However, when the common file system deals with the flat namespace, especially in the course of long-term use, the performance degenerates seriously. In this paper a new file system is proposed. XOBFS, which stands for extensible hashing object-based storage file system, uses fixed-length block allocation strategy and manages free block bitmap combination. Based on expanding hash manage object attribute, the same object attributes are stored in adjacent hash bucket. XOBFS applied in OSD has a lot of advantages. For example, the metadata has small scale, long-term performance is not degraded, and attribute of the object is managed effectively and so on. Test results show that big-object based XOBFS throughput rate is better than that of the traditional file system. XOBFS provides an effective method for storage management in OSD.