The author revised the definition of fossil energy land after analyzing the carbon circulation of terrain ecosystem. The new definition is forest and grassland required for the absorption carbon emission. And then, based on Net Ecosystem Production (NEP), the net deposition of carbon in vegetable body, the global average carbon absorption ability of forest and grassland were evaluated. In the end, combined with the data of heat conversion and carbon discharge, the footprint of fossil energy and electricity were re-calculated.