Focusing on the energy flow, Energy Return On Investment (EROI) is a method for evaluating energy resources exploitation, which is different from the Discounted Cash Flow (DCF) method taking money as the criterion of judgment. In this paper, we explore the correlation between EROI and DCF in the perspective of theory and mathematical formula. What is more, the judgment criteria of the two methods have been analyzed, and we take the Daqing oilfield as a case study. It is found that evaluating energy resources exploitation projects only by DCF is insufficient. From the perspective of social sustainable development, the society needs a limitless supply of energy, while DCF is difficult in ensuring the net energy outputs from the energy resources exploitation. Even though EROI can make up this, there is not a generally accepted judgment criterion for projects evaluation. For the same kind of energy resource, EROI should be used as an auxiliary index, combined with DCF, to evaluate the feasibility of energy resources exploitation.