Abstract: An incremental algorithm based on rough reduction for clustering data stream,named as RICStream (rough incremental clustering stream),was proposed to overcome the shortcoming of the CluStream algorithm,i.e.,the number of clusters must be predefined when it is used and the evolution of data stream can not be reflected efficiently to influence clustering results.With the guarantee of clustering accuracy,the RICStream adjusts the attributes of data stream incrementally to lead to the reduction of clustering time and computation cost.In order to store data stream a novel grid structure which can be adjusted incrementally was put forward.As a result,the changes of data stream can be efficiently reflected by clustering results.The experiments on real datasets and synthetic datasets show the applicability and validity of the RICStream.