Understanding the performance and microbial succession in nitrogen removal using fermentation liquid as carbon source can provide a practical basis for treating low C/N ratio wastewater. In this study, three typical fermentation liquids of food waste (FW) enriched with lactic acid (LA), propionic acid (PA), and butyric acid (BA) were added to high ammonia and high salt (HAHS) wastewater treatment process. Results showed that effluent TN decreased from 50 mg/L to around 15 mg/L with the influent concentration around 1000 mg/L after adding fermentation liquid enriched with LA and PA. In contrast, adding BA-rich fermentation liquid gradually deteriorated the nitrogen removal due to the nitrification process being impaired. Genus Thauera predominated in HAHS wastewater system via heterotrophic simultaneous nitrification and denitrification (SND) process. Utilization of LA- and PA-rich fermentation liquids induced the acclimation of other heterotrophic SND microbes and partially replaced Thauera. Conversely, BA-rich carbon source promoted the proliferation of heterotrophic denitrifying and ordinary heterotrophic microorganisms, thereby inhibiting nitrification process and ultimately leading to the failure of nitrogen removal. Meanwhile, the relative abundance of denitrification genes, including napAB, nirKS, norBC, and NosZ, annotated in Thauera exhibited the lowest relative abundance in BA-rich phase. This study provides valuable insights into the mechanism of using FW fermentation liquid as an alternative carbon source to promote nitrogen removal in HAHS wastewater.