Using the statistics data of the central bank 7 - day repo rate, the issuing rates of 3 - month and 1 - year central bank paper in open market operations from 2004 to 2006 , as well as the money market rates and medium - term treasury bond rates in the same period, this paper conducts statistical analysis, Cointegration Test and Causality Tests to find the impact of open market opera- tions on market interest rate for studying the effectiveness and limitation of open market operations.