Abstract: Aiming to improve the small file problem of a general distributed file system incloud storage,a file merging and prefetching strategy based on a users’access task is pro-posed that improves the PLSA model.Analyzing the relationships among the access tasks,applications,and access files the strategy merge small files on the basis of tasks and selectsprefetching files based the transition probability of the tasks.Efficiency model analysis andexperimental results of a digital city prototype system based on HDFS all show that the pro-posed strategy has a high prefetching hit ratio and can effectively reduce the metadata serv-ers’load and the response delay for users’request.