Oil-gas field development is a complicated system, and it is a difficult to make a decision of optimal development project. In this paper, a new method which is called fuzzy-grey-element relational decision-making analysis was proposed for evaluating and optimizing oil-gas field development project based on the fuzzy matter-element analysis combined with the grey system theory. Its gist is described as the fundamental element of project by the orderly three element group consisting of "a project, an index, whiten fuzzy-grey-quantity". This group is called the fuzzy-grey-element of project. The merits and demerits of various sorts of technical and economic indexes among the projects are considered comprehensively to appraise and optimize the development projects of oil-gas field, a good effect is acquired. A case study for optimizing gas development project in China showed that the result has a good agreement with practice. Therefore, this method is a general tool and can be used in other areas of petroleum, too.