This paper decomposed monetary growth uncertainty into two components:the untertainty which reflecting mac- roeconomic policy changes and the uncertainty about economic shocks by applying time-varying parameter Markov regime switch model and then investigated the effects of the two different sources of monetary growth uncertainty on macroeconom- ic activity based on monthly data from 1994 to 2005.Our conclusion are as follows:The uncertainty which economic shocks brought about is main source of monetary growth uncertainty and had negative effect on macroeconomic stability,on the other band the uncertainty which macroeconomic policy changes brought about had positive effect on macroeconomic stability.