To obtain high calorific biogas via anaerobic digestion without additional upgrading equipment, a two-phase pressurized biofilm system was built up, including a conventional continuously stirred tank reactor and a pressurized biofilm anaerobic reactor (PBAR). Four different pressure levels (0.3, 0.6, 1.0 and 1.7 MPa) were applied to the PBAR in sequence, with the organic loading rate maintained at 3.1 g-COD/L/d. Biogas production, gas composition, process stability parameters were measured. Results showed that with the pressure increasing from 0.3 MPa to 1.7 MPa, the pH value decreased from 7.22 +/- 0.19 to 6.98 +/- 0.05, the COD removal decreased from 93.0 +/- 0.9% to 79.7 +/- 1.2% and the methane content increased from 80.5 +/- 1.5% to 90.8 +/- 0.8%. Biogas with higher calorific value of 36.2 MJ/m(3) was obtained at a pressure of 1.7 MPa. Pressure showed a significant effect on biogas production and gas quality in methanogenesis reactor. (C) 2016 Elsevier Ltd. All rights reserved.