A method and an apparatus for implementing a storage function in a passive optical network (PON) system. On the basis of a LINK ID held by the data, data requiring storage, e.g. data making exclusive use of a wide bandwidth such as audiovisual data and large-volume data packages, are determined among all the data sent to an optical network unit. These data requiring storage are stored in a storage device installed in the optical network unit. In case the user requests data stored in the storage device, the stored data are transferred directly to the user, without any need to request and send these data for the second time via an IPTV server and the core network. It is possible to avoid duplicate transfers of data, and in particular to avoid duplicate transfers of data making exclusive use of a comparatively wide bandwidth such as audiovisual data and large-volume data packages, to improve the utilization factor of the downlink bandwidth, and to reduce flow congestion and data delays.