Abstract: Ammonia is a chemical energy storage carrier with great potential, and its use as a fuel is expected to promote the large-scale application of renewable energy. Fluidized beds, characterized by their high specific heat capacity and potential use of catalyst particles, offer advantages that facilitate ammonia ignition and stable combustion. However, combustion characteristics of ammonia in fluidized beds and effects of operating parameters remain unclear. In this study, a high-temperature fluidized bed setup is constructed to investigate the combustion characteristics of ammonia. The effects of equivalence ratio, oxygen volume fraction, and initial bed temperature on temperature distribution, emissions of nitrogen monoxide (NO), ammonia conversion rate and ammonia slip concentration are examined. The differences between premixed and diffusion combustion are also compared. The results indicate that under fuel-lean combustion, NO emissions are relatively high, while under fuel-rich combustion, NO emissions decrease, bed temperature drops and ammonia conversion rate decrease, ammonia slip concentration increases accordingly. Both bed temperature and NO emissions rise with increasing oxygen volume fraction. As initial bed temperature decreases, the region with the highest bed temperature after stable combustion shifts closer to the freeboard. For diffusion combustion, at a constant total ammonia input, an increase in oxygen volume fraction leads to reduced unburned ammonia. Under identical gas input parameters, there are no significant differences in bed temperature, NO emissions and ammonia conversation rate between diffusion and premixed combustion. This suggests that combustion of ammonia in a fluidized bed are not significantly affected by whether combustion is premixed or diffusive for the current experimental setup and operating parameters.