In the ever-increasing development of network storage technology, distributed RAID has been a hot topic for data reliability and availability. To solve the problem of distributed RAID technology, such as: parallel access difficulty, long rebuild time, small write update and strip alignment problem, we design and implement file level distributed RAID system (BW-FILERAID) based on Blue Whale File System (BWFS). Also we do the research on resource allocation strategy, page cache management with parity data, consistence maintenance, online extension of RAID group, error detect and rebuild and small write optimization in BW-FILERAID. According to the testing results, the writing performance of BW-FILERAID is better than Linux soft RAID about 5%~50%, and the reading performance is equivalent to the RAID0. And it also has excellent extensibility.