This study introduces an efficient query indexing method for processing data stream in RFID system. Several approaches to build an index on queries rather than data records, called a query index, have been proposed and are widely used to evaluate continuous queries over streaming data. However, it is difficult to use them for the RFID system because they suffer from data composed of a large number of segments. To solve this problem, our study defines concepts and properties of data in the RFID system and then proposes a transformation method that converts a group of segments into compressed data. This allows query index to store one object instead of the segments. We measure the performance improvement of the index by the proposed technique using experimental evaluation.