The invention provides a large power grid construction economic evaluation method, which comprises the following steps that: a two-stage evaluation system is built; proper evaluation indexes are selected; the evaluation is represented by comments in different degrees by fuzzy languages in fuzzy comprehensive evaluation; then, factors which are not easy to quantify are quantified by the fuzzy relationship synthesis principle; and an evaluated object is comprehensively evaluated from a plurality of factors. Particularly, evaluation indexes are firstly determined; then, the membership degree and the weight of the indexes are calculated; a fuzzy evaluation matrix and a weight vector are subjected to synthesis calculation; and finally, a fuzzy comprehensive evaluation result is obtained. The evaluation result which is not easy to quantify is quantified, and the evaluation result is simple and visual. The method provided by the invention has the advantages that a mathematic model is simple; the calculation is simple and convenient; the evaluation effect on multi-factor and multilayer complicated problems is better; and the method is applicable to the large power grid construction economic evaluation study.