Batch tests were carried out to analyze the effect of pH in the range Of 7-12 on the hydrolysis and acidification of sludge at room temperature. Ultrasonic pretreatment was conducted to disintegrate waste activated sludge (WAS) and accelerate WAS hydrolysis.. The experimental results showed that the sludge with ultrasonic pretreatment was readily degraded in the hydrolysis and acidification process, and more organic substances were released with increase of initial pH. The optimal initial pH for sludge acidification was 11, and the short chain fatty acids,(SCFAs) concentration reached about 1751 mg/L after 15 days of hydrolysis and acidification. Phosphorus release was investigated during hydrolysis and acidification at any adjustment The SCFAs mainly consisted of acetic and propionic, accounting for 74.6-84% of total SCFAs. Three microbial species, including Bacteroidetes, gamma-proteobacteria, and beta-proteobacteria, were involved in different pH environments of the hydrolysis and :acidification process, and, simultaneously, the three species were identified as being responsible for SCFA's accumulation and protein degradation. This study indicated that the combination of ultrasonic pretreatment, alkaline adjustment for hydrolysis, and acidification of WAS was an appropriate method for SOFAS accumulation and contributed to the demand of carbon source for WWTPs.