In this article, a defense method with watermarking to detect linear deception attack under Kullback-Leibler (K-L) divergence detector in cyber-physical system (CPS) is proposed. It is known that linear deception attacks can reduce the performance of remote estimator without being detected by the K-L divergence detector. In order to detect this kind of attack, we use watermarking to encrypt and decrypt data transmitted through wireless networks. When the attack does not exist, the transmitted data can be restored to ensure the remote estimation performance. In the presence of linear deception attacks, these data are marked with a watermarking so that they can assist the K-L divergence detector to discover the attack. The watermarking encryption method is proved to be helpful for K-L divergence detector to discover attack, or weaken the impact of the attack in different situations. Finally, numerical simulations are provided to further illustrate the results.