1. A system for sharing online storage services among multiple users, comprising: a user communication interface, for connecting to a client end corresponding to a first user; a file processing module, coupled to the user communication interface, wherein when the user communication interface receives a file upload request and a corresponding upload file from the client end, the file processing module searches for a personal online storage of the first user and a shared online storage of at least one related user of the first user and determines to upload the upload file to a partial online storage of the personal online storage and the shared online storage; and an online storage communication interface, coupled to the file processing module, for transferring the upload file to the partial online storage determined by the file processing module.