As a key parameter of fuel, the heat release characteristics of ammonia (NH3) flames under hydrogen (H-2)-enriched conditions constitute the emphasis of this research. The effect of H-2 addition on heat release characteristics of premixed laminar NH3 flames are numerically investigated by considering the detailed chemical mechanism. The NH3,O-2,H2O,NO, and N2O mole fraction distributions based on the Dagaut-Keromnes mechanism agree well with experimental results, thereby potentially providing repeatable and accurate outcomes with NH3 flames using this mechanism. The OH x N radical positively affects the net heat release rate at various equivalence ratios and H-2 addition ratios conditions. The chemical effect is evidently important at low H-2 addition ratios, while the transport effect becomes dominant at high H-2 addition ratios because of the high mobility of H-2. For the three top endothermic elementary reactions of NH3 flames, the contribution of R236: H + O-2=OH + O increases, while R171: H + NO(+M) = HNO(+M) and R240: H2O + O=OH + OH decrease with increasing H-2 addition ratios. Diverse key exothermic elementary reactions of NH3 flames occur at various equivalence ratios and different H-2 addition ratios. The large contribution of R128: N + NO=N-2+O at fuel-rich conditions can be applied to reduce NOx emissions of the NH3 flame under pure and H-2 addition conditions. (C) 2019 Elsevier Ltd. All rights reserved.