Based on an overall analysis of the methodology and technique for the description of terrain information representation, the TCI(Terrain Complexity Index),a new concept and quantification method for terrain complexity is proposed.TCI is a comprehensive index revealing the complexity and variation of true surface,which could be extracted via a calculation of an angle between two conjunct surfaces from a 3 by 3 cells based analysis window. Experiments shows that the TCI matrix derived from 1∶50 000 map scale DEMs could effectively represent the variation of the DEM based model surface. This research provides a good basis for constructing the conception system,as well as investigating the spatial distribution pattern of terrain information content.