To address the challenges of slow combustion speed and high NO_x emissions associated with ammonia as a zero-carbon fuel in engines, simulation research was conducted on the combustion and emission characteristics of  ammonia-hydrogen and ammonia-methane dual-fuel engines. One-dimensional simulation model （the core index error for model validation of less than 7%) was established using GT-POWER software based on the structural parameters of a 12.8 L natural gas engine. The effects of compression ratio and blending gas volume fraction on in-cylinder peak pressure (p_max), exhaust temperature, NO_x emissions, thermal efficiency were systematically investigated under different engine speeds. The results indicate that increasing both compression ratio and blending ratio can effectively enhance p_max and combustion speed, but would lead to lower exhaust temperature and higher NO_x emissions. Increasing the proportion of hydrogen or methane can significantly reduce fuel consumption rate and improve fuel economy.