Abstract: On the basis of the existing viewpoints down to date, the author tests that the time series of output in China has a unit root, the estimates suggest that the shocks to output are largely permanent. Then the impulse response functions are established to estimate the excessive persistence and according to the estimates, some conclusions are drawn: firstly, the shocks to output are persistent； Secondly, an unexpected change in real output of 1 persistent should change one‘s forecast by over 1 percent over a long horizon.