This study aimed to investigate the effect of acid-or alkali-treatment on volatile fatty acids (VFAs) production and microbiological mechanism during primary sludge anaerobic fermentation. Seven fermentation experiments were conducted at different pH (3-12). Results showed that the optimal pH was 10 for accumulation of VFAs. High-throughput sequencing results indicated that acid and alkali treatment could inhibit Erysipelotrichaceae_UCG-004 and norank_p_Aminicenantes, instead of promoting Pseudomonas and Tissierella at acidic and alkaline condition, respectively. Besides, molecular ecological networks (MENs) analysis and multi-variate canonical correspondence analysis (CCA) revealed that the microbial community interactions are significant different between acid and alkali treatment groups, and acetic acid was the most vital factor in the distinct bacterial community assemblages. Predictive functional profiling using marker gene sequences found that amino acid transport and metabolism was the most abundant metabolic type with 8.43-9.41%, and acid-and alkali-treatment did not benefit Stickland reaction.