To improve the dewaterability of municipal sludge, the Acidithiobacillus ferrooxidans (At·fXJF8) cultivated in a laboratory-scale plug flow reactor (68 L) were used, which had efficient biomineralization and biological acidification. Chemical parameters of pH, specific resistance, suction filter mud cake moisture content of the municipal sludge was determined pre-and after dehydration etc. The optimum operation parameters of the reactor was: SRT 3.7 d, Fe(Ⅱ) dosage 2.11 g·L-1, reflux ratio 80%. Experiment result showed that the pH of the sludge decreased from 7.22 (stat-up stage) to 2.95 (steady stage) after the dewatering, and the specific resistance to filtration (SRF) of sludge decreased from initial (4.2±0.59)×10¹² m·kg-1 to the final (0.55±0.11)×10¹² m·kg-1. Ferrous oxidation rate kept above 96% in the whole running process. At the condition of 0.05 MPa pressure from the suction filtration, water content of the sludge decreased from 80% to 68%. This paper developed a new method for the sewage sludge dewaterability with the bio-acidification and ferrous oxidation by At· fXJF8.