Chemical looping hydrogen production using natural iron ore has attracted extensive attention. However, the greatest challenge is the relatively low deep-reduction rate of iron ore, significantly affecting H-2 production. A new biomass ash-modified iron ore has been developed to enhance the deep reduction of oxygen carrier and hydrogen production. Chemical looping hydrogen production is experimentally carried out in a fluidized bed using CO as fuel. The effect of several parameters is evaluated, including ash type, ash content, reaction temperature and cycle number. Results indicate that the performance of the modified iron ore primarily depends on ash type. The Si-rich rice stalk ash causes serious particle sintering, resulting in reactivity deterioration of oxygen carrier. Contrarily, new formations of K-Fe-O compound enhance the deep reduction of other ash-decorated oxygen carriers increasing H-2 yield. Nevertheless, the co-existing negative effect of ash on oxygen carrier reduction and H-2 production also appears when the content of rape stalk ash and wheat stalk ash exceeds 10%. The 15% sunflower ash-decorated iron ore exhibits a relatively superior performance, and the elevated temperature promotes H-2 yield and H-2 purity reaches the maximum 99.57% at 900 degrees C. The selected 15% sunflower ash-decorated iron ore exhibits a stable performance for promoting H-2 production.