The combustion noise of a biogas and diesel dual-fuel engine is evaluated by time region and frequency region comprehensively. The effects of engine rotate speed, engine load, the advance angles of fuel supply and the biogas replacement rate on the combustion noise were analyzed. The result shows that the total combustion sound pressure level is less affected by the engine rotate speed at 21°CA BTDC (crankshaft angle before top dead center). The combustion sound pressure level increases with the increasing of the engine load at the same engine rotate speed. The cylinder pressures of the two types of engines change markedly when the fuel supply advance angle increases to 24°CA BTDC. The increasing of engine rotate speed results in the oscillation of the cylinder pressure at high frequencies, and the cylinder pressure increases with the increasing of engine load at low and middle frequencies.