In this research, the computational fluid dynamics (CFD) coupled with reduced chemical kinetic model was applied to study the combustion process and emissions characteristics of a NG-diesel dual fuel engine at various injector spray angles. The model was validated by measured data of in-cylinder pressure, heat release rate (HRR) and emissions (nitrogen oxide (NOx), hydrocarbons (HC), carbon monoxide (CO)) in the NG-diesel dual fuel engine. The validated CFD models were used to investigate the immediate process of combustion and emissions of NG-diesel dual fuel engine with the variation of spray angle. The results showed that the peak cylinder pressure increases as the spray angle increases from 60 to 140, but slightly decreases if the spray angle continues to increase to 160. Except for the condition of 1000 rpm and 50% load, the start of combustion (SOC), CA50, 10-50% combustion duration, CA90, 50-90% combustion duration and 10-90% combustion duration decrease as the spray angle increases from 60 to 120, and keep minor fluctuations when the spray angle increases from 120 degrees to 160 degrees. The NOx emissions ascend when the spray angle increases from 60 degrees to 140 degrees and changes little if it continues to increase from 140 degrees to 160 degrees. Nevertheless, the unburned methane is almost unchangeable at 1000 rpm and 100% load. When the spray angle ranges between 120 degrees and 160 degrees, the CO emissions keep at a lower level. All these have provided visual data and theoretical guidance for improving the combustion and emissions performance of NG-diesel dual fuel engine.