The contribution of personal consumption expenditure to U.S. economic growth decreased and the slowdown of the gross private domestic investment indicate that enterprises became less optimistic to the future in the past year. Net export and government expenditure are also promote grow effectively against the background of the subdued pace of foreign economic growth and huge public debt burden. Even through fundamental economic indexes still in good shape，future growth expectation held down by the flattened unemployment rate，the slowed pace of improvement of labor market condition，the fell back of consumer confidence index after it reach its peak，and remained relative stable of longer-run inflation expectation. The uncertainty of the economic growth warrant only gradual future increase in the federal funds rate. It is expected that the U.S. economy will grow at a slower pace in 2016 and 2017.