The two major features of the relationship between the U.S. and Taiwan are its being unequal and nonofficial. These two features constrain U.S.-Taiwan political, economic, and military cooperation. This research constructs two ideal type operational processes of U.S.- Taiwan unequal cooperation, and formulates qualitative and quantitative indicators for accessing it. By applying these indicators, this study evaluates U.S.-Taiwan political, economic and military cooperation from the time of the Chen Shui-bian administration to that of Ma Ying-jeou. The study finds that U.S.-Taiwan cooperation is much better during Ma's administration than that in Chen's. The author argues that if Taiwan challenged the U.S. policy constraints, bottomlines or declined U.S. demands, this would lead to a setback in the relationship between the U.S. and Taiwan. This study also finds that among the various forms of cooperation, political cooperation is most easily influenced by negative factors. Economic cooperation is the second most easily influenced form. Military cooperation is least easily influenced because of U.S. strategic interest considerations.