TIN DEM data of the key areas have significant protection value. According to the data organization form, this paper proposes a new method of TIN DEM information disguising based on permutation-substitution theory which is a classical theory in cryptography. Firstly, the original data is permuted using the chaotic sequence which is generated by Tent map in frequency domain. Secondly, in the basis of Chinese remainder theorem, the final disguised data could be obtained by the numerical substitution in spatial domain, and the method of information reduction is also discussed in this paper. Finally, the disguising effectiveness and security performance of the method are validated by analyzing the experiments, which can meet the requirements of TIN DEM information disguising and also could guarantee the storage and transmission security for the TIN DEM data.