Wetland quality is a critical factor in determining values of wetland goods and services. However, in many studies on wetland valuation, wetland quality has been ignored. While those studies might give useful information to the local people for decision-making, their lack of wetland quality information may lead to the difficulty in integrating wetland quality into a cross-studies research like meta-analysis. In a meta-analysis, a statistical regression function needs withdrawing from those individual studies for analysis and prediction. This research introduces the wetland quality factor, a critical but frequently missed factor, into a meta-analysis and simultaneously considers other influential factors, such as study method, socio-economic state and other wetland site characteristics, as well. Thus, a more accurate and valid meta-regression function is expected. Due to no obvious quality information in primary studies, we extract two kinds of wetland states from the study context as relative but globally consistent quality measurement to use in the analysis, as the first step to explore the effect of wetland quality on values of ecosystem services.