Invasion of salt into wastewater treatment plants can change intracellular osmotic pressure of bacteria and influence microbial activity and degradation ability in bio-treating system with activated sludge.Effect of salinity on treatment efficiency was simulated based on MUCT process for treating real saline sewage.A model was constructed by combining the pollutant degradation kinetics and the inhibition kinetics，by which the salt toxicity on functional microorganisms in activated sludge was evaluated.The results showed that intrusion of salt can cause its activity loss and disrupt normal removal of pollutants.And this toxicity can reduce significantly respiration of aerobic microorganisms，and evaluation on the effect of salt toxicity，based on the respiration inhibition，can be overestimated，while based on pollutant degradation rate it can properly be related to treatment efficiency and the real situation of treatment system.In this study，IC50 values of salt inhibition obtained for the degradation of organics heterotroph，nitrifiers and denitrifiers were 20.64 g·L-1，11.61 g·L-1，and 10.88 g·L-1，respectively.