A mathematical model was developed in this paper to describe the nonylphenol (NP) accumulation in the effluent of a wastewater recycling system. The model quantitatively presented the relationships among the NP concentrations in the raw wastewater and the system effluent, the number of wastewater recycling cycles, the water recycling ratio, the system NP removal efficiency, and the NP accumulation factor. The mathematical model was then verified through experimental modeling of a wastewater recycling process, and it was indicated that the Pearson correlation coefficient between mathematical simulation and experimental modeling results was 0.652. The study results indicated that the NP accumulation factor of a wastewater recycling system would approach a constant for large number of wastewater recycling cycles given the wastewater recycling ratio and system NP removal efficiency. The results also revealed that the NP concentration in the effluent increased with the wastewater recycling ratio given the system NP removal efficiency, and the increase of NP removal efficiency would decrease the NP accumulation in the system effluent under a given wastewater recycling ratio condition. The model was then applied to compute the maximum wastewater recycling ratio, predict reclaimed water quality and direct the design and management of sewage recycling systems in China.