With the development of wireless communication technology and positioning technology, trajectory data emerge in large quantities. Similarity measurement is used in the query and analysis of trajectory data. In this paper, an improved similarity measure- ment is proposed. By introducing the negative correlation between the distance of points and the similarity into the real sequence ed- iting distance, the robustness to noise is preserved and the sensitivity to difference is improved. We apply different similarity mea- sures to the trajectory privacy protection method based on cluster-reconstruction, and verify the effectiveness of the proposed trajec- tory similarity measure by experiment on the real data and the synthetic data.