Abstract: This paper put forwards a new method within the “counterfactual” framework to estimate the effects of the macroeconomic policy when taking into account the existing difficulties of constructing “counter facts” by using macro data; and as an application, it gives an ex post estimation of the economic growth effect of the “four trillion” investment implemented by Chinese government since the third quarter of 2008. The result of the study shows that the investment contributed to the real GDP growth by 0.93 percentage in 2009, while the effect reversed quickly in 2010. It also indicates that the “four trillion” investment has indeed played a considerable role in preventing China’s economy from slipping into recession during the global financial crisis, but it is not necessary to ensure the growth goal of eight percentage that once launched in 2009, which will not affect the economy significantly in the long run.

Key words: counterfactual; the “four trillion” investment; economic growth effect; ex post evaluation