In this paper, experiments and numerical calculations were conducted to investigate the effect of H-2 addition on dimethyl ether (DME) jet diffusion flame behaviors, in terms of thermal and chemical structures, reaction zone size, flame entrainment, and NOx and CO emission indices. A wide range of H-2 additions from pure DME to pure H-2 were involved herein, while maintaining the volumetric flow rate of fuel mixture constant. The results indicate that when H-2 mole fraction in the fuel mixture exceeded 60%, the blended fuel was converted to H-2-dominated. Besides, the flames behaved rather distinctly at the DME- and H-2-dominated regimes. With the increment in H-2 addition, flame temperature, H-2, H, O, and OH concentrations increased gradually, but concentrations of the intermediate hydrocarbons (such as CO, CH2O, CH2, and CH3) decreased on the contrary. Additionally, after the flame became H-2-dominated, the species concentrations varied increasingly quickly with H-2 addition. The reaction zone length and width decreased nearly linearly with H-2 addition at the DME- and H-2-dominated regimes. But the decreasing speed of reaction zone length became faster after the flame was converted to H-2-dominated. At the DME-dominated regime, the dependence of flame entrainment coefficient (C-e) on H-2 addition was rather small. While at the H-2-dominated regime, C-e increased increasingly quickly with H-2 addition. Moreover, with the increment in H-2 addition, NOx emission index increased and CO emission index decreased gradually. In addition, at the DME-dominated regime, NOx emission index increased fairly slowly with H-2 addition; while at the H-2-dominated regime, it increased significantly. The optimal H-2 addition to DME was 60 vol.% in the practical engineering. (C) 2014 Elsevier Ltd. All rights reserved.