Abstract: To investigate the influence mechanism of hydrogen blending ratios on combustion characteristics of an aviation ammonia-hydrogen rotary engine under high-altitude conditions， a three-dimensional simulation model was developed in CONVERGE based on an in-cylinder swash-plate rotary engine. This model was employed to analyze combustion and emission processes at hydrogen blending ratios of 13%~29% under constant operating condition， i.e. 6 000 m altitude， 6 000 r/min engine speed， 1.2 equivalence ratio and -20° ignition timing. Simulation results showed that increasing hydrogen blending ratios significantly improved the flame propagation velocity. The peak in-cylinder pressure increased from 2.7 MPa at 13% hydrogen blending ratio to 6.3 MPa at 29% hydrogen blending ratio， and the peak exothermic rate increased from 3 J/（°）to 23 J/（°）. The combustion duration was shortened， and the generation of NO increased with the increase in the hydrogen blending ratio， while the emissions of NO₂ and unburned ammonia decreased. Elevating hydrogen blending ratios can effectively optimize the combustion phase， and enhance the combustion stability， though increased NO emissions should be considered.