To improve the ignition and combustion performance of NH₃ in engines, blending it with the high-reactivity-fuel dimethyl ether (DME) is an effective strategy. This study conducts simulations of NH₃/DME/air premixed laminar flames to investigate the effects of DME addition on key combustion characteristics, including laminar flame speed, reaction pathways, and NO formation. The results show that both the adiabatic flame temperature and the laminar flame speed increase significantly with higher DME blending ratios. A strong correlation is observed between laminar flame speed and the concentration of reactive free radicals, suggesting that the increased radical concentration due to DME is the main contributor to the enhanced flame speed. Furthermore, the normalized NO concentration in the flame rises significantly with increasing DME content, reaching approximately 50% when the DME blending ratio reaches 80%. Reaction pathway analysis indicates that DME addition inhibits the conversion of nitrogen species to N₂, thereby leading to increased NO emissions. Sensitivity analysis shows that DME significantly alters the dominant elementary reactions. As the DME ratio increases, the sensitivity of nitrogen-group reactions considerably declines, while hydrogen- and carbon-group reactions increasingly govern the combustion process of the blended fuel.