In this paper, a framework for WAMS communication system security assessment is presented. Firstly, it divided the communication systems of WAMS into several subcomponents according to ISO/IEC 17799, and then associated the assets' property by the Architecture Theory Diagrams (ATD). Secondly, the AHP is introduced to build the assessment hierarchy and distribute the index weight. At last, the data of subcomponents is aggregated by the D-S algorithm. In this way, it compensates for the side-effects of the inherent uncertainties of WAMS and makes the result more accurate. At last a case study shows that the framework and evaluation methods presented in this paper have an instructional significance on improving the information security of WAMS. They also can be applied in other communication systems of power systems.