The hydraulic characteristics of constructed wetland are vital to its performance for pollutant removal. Hydraulic characteristics of a pilot scale vertical flow constructed wetland were studied by tracer experiments with the method of moments (MoM) analyzing. From the residence-time distribution (RTD) of tracer during the experiment, the mean detention time, average water velocity and dispersion coefficients were obtained for the constructed wetland. The results showed that the mean residence time was approximately 15% shorter than nominal residence time indicating 85% of total available pore volume was active in pollutant removal processes. The two peaks observed on the RTD curves suggested short-circuiting flows or dead zones exist in the constructed wetland. The relatively large Peclet number of 11.8 suggested that dispersive processes dominated in the tracer movement. Comparison of tracer profiles at different sampling locations indicated that large amount of tracer transported through the upper portion of the constructed wetland.