Net primary production (NPP) is a central and fundamental carbon-related term in global change studies. We proposed a top-down method to quantifying forest NPP which overcomes the deficits of the traditional bottom-up method. The new top-down method combines eddy flux data, climate variables, tree inventory and metabolic theory. Our method was tested in six forests and provides reliable annual NPP estimations which are consistent with bottom-up results. Carbon use efficiency also supports this new method. Taking advantage of fine temporal resolution of our top-down method, we examined whether and confirmed NPP was well correlated with leaf area index at a seasonal scale, as suggested by past studies. The potential value of our new method as a standard NPP method is high because of the world-wide network on eddy tower and inventory plot, however further data of performance of the new method is needed to fully evaluate its performance under different conditions.