Monetary policy has different impacts on economic activities in business cycle. This is noted by the asymmetry of monetary policy. By detrending the time series and using the GARCH model with asymmetry , we find out in China that tight monetary policy slow the economy in the boom more than easy monetary policy accelerates the economy in the recession. Therefore , in the recession period of business cycle , we should take the robust monetary policy to avoid the financial risk and prevent the inflation , take the active fiscal po