Abstract: Text information hiding technology is applied in protection of copyright and integrity of digital media. Under the processing of word segmentation and part-of-speech tagging, a natural language sentence is transformed into a sequence of part of speech symbol, thus the parity of sequence’s inverse order number is used for information hiding. The properties of sequence’s parity under the transformation of symbols’ exchanging, adding and deleting is proved. According to the information hidden, the sequence of part of speech symbol is properly transformed firstly, and the modification of sentence is directed by the transformed sequence, so the feasibility of sentence’s modification is theoretically ensured. Furthermore, aimless modification on natural language sentence can be avoided.