Abstract: This paper starts with principle of economic evaluation of the third resource assessment. It introduces application of "method of the least oil field reserve scale" in study of economic evaluation of the third resource assessment in detail. And it analyzes respective characteristics of dynamic and static state models of "method of the least oil field reserve scale". At last, it combines oil field practice and gets the least oil field reserve scale of oil field in different oil price.It also makes sensitivity analysis to several influential factors of the least oil field reserve scale. It offers gist for instructing next exploration.