Abstract: A new watermark technology for databases based on (t,n) threshold was presented in this paper．Firstly,(t,n) threshold is used to divide watermark into some shade shares．Secondly,the tuples of relational database are marked by their hash values．The position for watermark embedding is based on the parity deference between mark and Most Significant Bits of the attributes．Finally,the watermark information is embedded into the numerical attributes of the database based on a new matching rule．Experimental results show that this algorithm is safe and effective to prevent various of attacks.

Key words: Database,Threshold,Lagreange interpolation formula,Watermark