The treatment efficiency of constructed wetlands (CWs) is highly dependent on the stability of the hydraulic flow patterns. To date, general technologies used to study hydraulic flow patterns of CWs mainly include tracer method, model simulation and velocity measurement, which are either expensive, empirical, or having secondary pollution. In this study, a new technology, which was based on the isotopic composition variation in CWs, was applied to detect the hydraulic flow patterns of two different CWs. Results showed that the hydraulic flow patterns of the two studied wetlands could be detected effectively by using hydrogen and oxygen isotopes. Furthermore, the locations of stagnant areas (SAS) and preferential flow areas (PFAs) were also determined. Significant regional difference in isotopic composition existed inside each CW, and two wetland design suggestions are proposed after hydraulic analysis. One is that the influent of CWs is supposed to be distributed uniformly, and another piece of advice is that the vegetation in the direction perpendicular to water flow should be maintained at the same types and density. (C) 2016 Elsevier B.V. All rights reserved.