Nitrogen removal performance and key enzyme activities of “Candidatus Brocadia sinica” with sorbitol addition were investigated in nitrogen-laden saline wastewater treatment. Nitrogen removal through “Candidatus Brocadia sinica” first increased and then decreased with sorbitol addition. Optimal ammonia removal rate and nitrite removal rate were 0.53 and 0.67 kg/(m3·d) at 0.8 mM sorbitol, which increased by 39.5% and 71.8%, respectively. Moreover, appropriate sorbitol content could resist salt stress and decrease extracellular polymeric substances content of “Candidatus Brocadia sinica”. Independent of sorbitol concentration, hydrazine dehydrogenase and nitrite reductase activities were enhanced about 1.37–2.36 folds. Remodified Logistic model was the most appropriate to analyze nitrogen removal process with sorbitol addition. Fitted Rmax (%/h) could be converted into Vmax (kg/(m3·d)) to predict optimal substrate conversion rates of “Candidatus Brocadia sinica” treating nitrogen-laden saline wastewater with various sorbitol contents.