Chemical looping hydrogen generation (CLHG) consists of an oxidation process, a reduction process, and a hydrogen generation process. Achieving deep reduction of the oxygen carrier is the challenge for the CLHG process. In this paper, experiments on CLHG using K-modified iron ore as an oxygen carrier and CO as a fuel were carried out in a laboratory scale fluidized bed reactor. A high temperature improved the reduction reactivity. However, at the same reduction condition, a higher temperature did not improve the hydrogen generation process, which means that a higher temperature mainly benefited the reduction process and then elevated hydrogen generation in a CLHG process. Adding KNO3 improved the rate of reduction and hydrogen generation. With the KNO3 loading in iron ore increasing from 0 to 10%, not only the carbon conversion but also the hydrogen production was accelerated. A high KNO3 loading in iron ore can also maintain longer reaction time. The 10% K-modified iron ore could decrease carbon deposition. The scanning electron microscopy analysis and the cycling experiments indicated that adding K could keep the porous structure of the oxygen carrier and the K-modified iron ore was a stable catalyst in the CLHG process.