In view of the shortcomings of the previous NH3/DME reaction mechanism, combustion reaction mechanisms of NH3, DME, and NH3/DME were constructed by using the minimized reaction network method under the condition of determining the number of chemical species. The mechanism of the construction had a simple reaction network using reversible reaction form, and the reaction direction was unified in form. The mechanism construction process of NH3, DME, and NH3/DME avoided the mechanism simplification step, which can greatly reduce the number of species and reactions. Finally, the NH3 chemical reaction mechanism containing 18 species and 43 reactions, the DME chemical reaction mechanism containing 34 species and 51 reactions, and the NH3/DME chemical reaction mechanism containing 44 species and 93 reactions were developed. The laminar burning velocity and ignition delay time of NH3, NH3/H2, DME, DME/H2, and NH3/DME combustion under a wide range of initial conditions were validated. The results showed that the errors of laminar burning velocity and ignition delay time compared with the experimental values were within 10% under most initial conditions, which verifies the reliability and practicability of each combustion reaction mechanism.