In this article, the interaction between acetic acid and methanogenic bacteria activity was investigated. The dry anaerobic digestion was conducted with four lab-scale reactors (R1-R4) and acetic acid at different concentrations were fed as additional substrate to R1-R4. The results showed that the population of acetocastic-utilizing methanogens decreased along with the increasing of acetic acid, in which the concentration was above 120,000 mg.L-1 during the stable stage with coefficient of 0.8984. The activity of methanogenic microorganisms in R2 was the best of all reactors. The maximal biogas production rate in R2 was 1.73 m(3) m(-3) day(-1) with the methane content of 55%.