The use of RFID tag which identifies a thing and an object will be expanded with progress of ubiquitous society, and it is supposed that the various RFID-based services will be provided in the near future. Therefore, it is necessary to study how to construct RFID network system as a social infrastructure like the Internet. This paper proposes the virtualization method of RFID tag network system to enable the same physical RFID network system to be used by multiple different service systems. The system virtualization not only reduces the system cost but also can dramatically reduce the installation space of physical readers and the operation cost. It is proposed that all equipments in the RFID network system except radio tag could be shared with the conventional virtual technologies for servers or networks. It is also proposed to add two new identifiers, in order to improve user convenience in the infra-structured RFID network system. One is dasiasystem IDpsila to keep the association between a virtual reader element and a physical RFID tag, and the other is dasiapolicy numberpsila that specifies the conditional tag ID processing.