To investigate the flat-panel display characteristic, and improve display industry development. As the international standards developed or adopted, ambient contrast ratio of display is a significance indicator. In this paper, we measured the ambient contrast ratio of display by several methods, included integrating sphere method, spectrum analysis method and sampling method, contrasted with each result. They measured the same sample with different methods. We found this test method could be used to get the ambient contrast ratio in any lighting environment. It can be obtained widely in display industry, also in the international standards.