Abstract: Constructed wetland is a quite productive ecosystem that can provide very abundant services for people. Most of the previous researches on constructed wetland focused on its purification efficiency and working mechanism. However, there was a lack of one kind of systematic and comprehensive evaluating system on constructed wetland ecosystem service. A new method, comprehensive index of ecosystem service of constructed wetland, based on analytic hierarchy process and fuzzy membership function method, was developed to valuate ecosystem service of constructed wetland. It could be developed by several steps as follows: Firstly, a comprehensive evaluation model of constructed wetland and its indicator system were set up. Secondly, specialists' marking method was used to construct the judgment matrices of criterion and alternatives. Thirdly, the consistency of matrices was tested until they accorded with the test rule. Fourthly, appropriate fuzzy membership functions of the alternatives' indicators and its relative parameters were built up. Fifthly, the BOFP-CW was selected as an example, and the original values of relative indicators were calculated. Sixthly, according to its original values and fuzzy membership functions the fuzzy memberships were computed. Seventhly, the final ranking of criterion and alternatives of comprehensive evaluation of constructed wetland ecosystem service were conducted, and its final priorities were computed. Finally, multiplied the final priorities by fuzzy memberships, and the total of the result was comprehensive index of BOFP-CW ecosystem service which was calculated at 0.7848 points (the full mark was 1, and 0.6 was up to grade). This score indicated that the ecosystem service of BOFP constructed wetland was of great worth. It could serve people well by purifying water, providing habitat, regulating microclimate, entertaining and educating citizens and working as scientific research base. The comprehensive evaluation offered a method to compare the quality of ecosystem service on different constructed wetland or the same constructed wetland in different period, respectively. It was of great significance for the research, improvement, construction, running and maintenance of constructed wetland.