Abstract: Black liquor of straw pulp was treated in two-phase anaerobic digestion process.After biokinetic analysis of experimental data,the results showed that the modified Monod Equation could be used to describe the substrate degradation process in the methane phase.The concentration of nonbiodegradable materials (COD) was 1212 mg/L from the model when the COD of influent in acidification phase was 766112958mg/L and the COD of influent in methane phase or the effluent in acidification phase was 53218957mg/L.Maximum COD removal efficiency was 8647% in methane phase at similar conditions of experiments.