Protozoa are ideal biological indicators of pollution and toxicity. The microbial communities monitor method, or Polyurethane Foam Unit (PFU), is widely used to assess the extent of water pollution due to its rapidity and accuracy. The Yancheng coastal chemical industrial zone, located in northern Jiangsu Province, is the largest special park approved for construction by the environmental administration of Jiangsu Province. This sector primarily oversees the development of pharmaceutical and chemical products. Wastewater discharged as part of such chemical manufacturing processes is an important source of water pollution and can potentially devastate water environments. Using the protozoan communities in the clear water near the industrial zone as source species, the static toxicity of the chemical wastewater was evaluated by PFU. Results showed that protozoan communities are very sensitive to effective concentration (EC) variations in the chemical wastewater. Under prolonged exposure to toxin at lower EC, rapid increases in protozoan species diversity and colonized species indices, as well as colonization rate, were observed. At higher EC, the protozoan species diversity index increased slowly (or even decreased) while the colonized species index and colonization rate were reduced, indicating that high chemical wastewater EC exerts strong biological stress on water-inhabiting protozoa. Microbial communities exposed to low toxic stress from chemical wastewater eventually adapt and reach maturity. To characterize the protozoan colonization process, the number of protozoan species required to achieve balance S_eq, the colonization rate G and the time required to achieve 90% S_eq were studied in-depth. Among these three functional parameters (S_eq, G and T_90%), S_eq was found to negatively correlate with the chemical wastewater EC, while G first negatively and later positively correlated with the chemical wastewater EC. The regression equation is S_eq= -0.141 EC+19.05 (R²=0. 941,P<0. 01). The EC₅, EC₂₀ and EC₅₀, determined from the above regression equation, were 7.1%, 27.3%, and 67.7%, respectively. Therefore, the relative safe concentration and maximum acceptable toxicant concentration (MATC) of the wastewater for the protozoan communities are 7.1% and 27.3%, respectively. To safely discharge this wastewater, more than 72.7% of the toxins must be removed by further processing. Our data may aid further research regarding the effects of toxic chemical wastewater effluent on water environmental indicators, and may guide the supervision and control of chemical wastewater pollution within the Yancheng coastal chemical industrial zone.