Hydrogen production by ammonia decomposition faces the problem of low NH_3 conversion and the activity of ammonia decomposition catalysts needs to be improved. Molecular sieves, with large specific surface areas and rich pore structures, can be used as excellent carriers for ammonia decomposition catalysts to enhance their activity. However, the influence of the carrier properties of molecular sieves on ammonia decomposition is not clear. This work investigated the effect of Co-based catalysts with different molecular sieve carriers (ZSM-5, SBA-15, MCM-41) on the hydrogen decomposition reaction of ammonia. Co/SBA-15 exhibited the best ammonia decomposition activity. Combining the catalytic activity and characterization results, we found that the carrier of the ammonia decomposition catalyst should have a large specific surface area, a rich pore structure with appropriate pore sizes, small catalyst particle sizes , a small number of acidic sites, and weak acidic strength. The active sites of the ammonia decomposition reaction were in the metal state, and the H_2 reduction treatment of the catalyst before the reaction could effectively improve its ammonia decomposition activity. Meanwhile, compared with the other two molecular sieve catalysts, the Co/SBA-15 catalyst had a lower apparent activation energy. Additionally, the Co/SBA-15 catalyst exhibited excellent catalytic stability and reproducibility. Finally, in-situ DRlFT experiments on the Co/SBA-15 catalyst revealed the enrichment of -NH and -NH_2 intermediates on its surface, suggesting that the rate-limiting step of the ammonia decomposition reaction might be the recombinant desorption of N atoms from the adsorbed state. This study elucidates the influence of the physicochemical properties of catalyst carriers on the performance of the ammonia decomposition hydrogen production reaction and provides some theoretical guidance for the selection of catalyst carriers for ammonia decomposition.