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.