Based on the analysis of typical existing pollutant removal models for constructed wetlands, this paper presents a generalized expression of various models in terms of differential equations. The proposed generalized expression can not only embrace most existing models as special cases but also interpret the transitions from one model to another. Potential application of the generalized expression was exemplified through the case of NH+4 and BOD₅ degradation in subsurface flow constructed wetlands. It was shown that the generalized expression is helpful to reveal the pollutant removal mechanism, and thus it is good for development of more accurate models.