Proceeding of the Joint International Symposium on Deformatuon Monitoring. 2-4 November, 2011. Hong Kong. China. Report. This paper firstly analyzes the theory of coordinate similarity transformation, and a novel method of stability analysis for datum points applied in high-precision GPS deformation monitoring network is then put forward. The coordinate similarity transformation model is adopted to calculate transformation parameters for station coordinates of two adjacent periods. By comparing the transformed results and the network adjustment solutions, the station stability is verified. In order to judge the stability of stations, "the threshold of station stability" and "statistical test based on variance ratio" are developed. It is applied to stability analysis of three periods' datum points in an A-order GPS deformation monitoring network for hydropower station to verify the feasibility and effectiveness of this method.