CASM is the abbreviation of Coherent Adaptive Subcarrier Modulation. CASM is one of the Combining Method of signals. It will be used in GALILEO satellite navigation system. In this paper, on the base of analyzing and studying CASM in theory, do some research in connection with the used case of CASM in E1 signals of GALILEO system. It is shown from the result that CASM is an effectual Combining Method of signals.