The study compared the differences in VFAs production between raw sludge and thermal hydrolyzed sludge (TH-sludge) at different temperature (35 degrees C and 55 degrees C) in four semi-continuous acidification reactors. Optimal VFAs yield was obtained from TH-sludge at 35 degrees C (0.22 gVFA(COD)/gVS), 44.6% higher than raw sludge at 35 degrees C, since the advantage of TH-sludge in SCOD solubilization overcame its disadvantage of lower carbon biodegradability. Moreover, high temperature (55 degrees C) was proved to aid the acidification of raw sludge by 15.7% (in Y-VFAs), but inhibit that of TH-sludge by 12.2%, mainly due to the suppressed microbial activities under heat. Microbial community analysis showed that TH-sludge had a larger proportion of acidogenic microbes than raw sludge, mainly attributing to the increase of Selenomonadales (37.3% vs. 3.7%); high temperature enriched thermophilic proteolytic microbes, Anaerobaculum and Coprothermobacter. Finally, optimal acidified liquid from TH-sludge at 35 degrees C was applied for PHAs production and achieved a competitive yield of 34.6% PHAs/DCW.