Benefit assessment is the prerequisite for making scientific policy of land consolidation. Some practices severely affected the sustainable using of land resources for shortage of the standard and restraint of ecological benefit. This paper analyzed the concept and the items of land consolidation and discussed the important role of ecological benefit assessment. Through the identification of effect boundary of land consolidation and based on the emergy theory, this paper proposed a method to assess the ecological benefit of land consolidation which took the quantitative change of free emergy investment from natural ecosystem to product or service as a token of ecological benefit of land consolidation. Also the assessment formulas were established.