A two-phase pressurized biofilm (TPPB) system, including a continuously stirred tank reactor (CSTR) and a pressurized biofilm anaerobic reactor (PBAR), was used to produce high calorific biogas without additional upgrading equipment. The influence of organic loading rate (OLR) on biogas and methane production performance was investigated. Three different OLR levels (4, 5, and 6 g-COD/L/d) were applied to the PBAR in sequence. The headspace pressure of PBAR was controlled at 1.0 MPa. Biogas production, gas composition, and process stability parameters were measured. Results found that the highest methane yield of 332.8 mL/g-COD was obtained at OLR of 5 g-COD/L/d. As compared to approximately 90% methane concentration at OLR of 3.1 g-COD/L/d, the methane content in produced biogas was only 76% at OLR of 5.0 g-COD/L/d. The pH value in the pressurized reactor has an important impact on the quality of produced biogas. Further study should focus on the solution strategies of maintaining suitable pH under higher pressure and higher OLR.