A new multi-zone combustion and heat release model has been developed based on the first law of thermodynamics and combustion characteristics of dual-fuel engine. Also the differential equations calculated the heat release rate of the combustion have been deduced and applied on a biogas diesel dual-fuel engine. The research results showed that the top heat release rate of dual-fuel engines was larger than that of the original diesel engines, however the ignition delay period and the combustion duration increased.