The current trend is modeling the simple subsurface constructed wetlands for improving the efficiency of the wastewater purification process by increasing the complexity of the constructed wetland system. This paper reviews some published non-mechanistic and mechanistic models for a constructed wetland. Several authors aimed to model the hydraulic behavior of the system including tracer experiments only. There are few published models the biochemical transformation and degradation processes that occur in the complex system subsurface flow constructed wetland. Models describing reactive transport underwater flow saturated conditions can only be used to model horizontal flow constructed wetlands. Some models are reviewed in these categories that use either a series or a network of ideal reactors (continuously stirred tank reactor and /or plug flow reactors) or are only applicable for constant flow rates to model water flow. Transformation and removal processes are described for organic matter and/or nitrogen. Modeling vertical flow constructed wetland with intermittent loading requires transient variably saturated flow models as these systems are highly dynamic, which adds to the complexity of the overall system. Based on this review need to modeling of constructed wetlands from time to time.