The effects of humic acid (HA) on the movement and transformation of potassium (K) in a cinnamon soil were studied through an incubation experiment by using soil column. Compared with solely application of KCl, the addition of HA did not change the diffusion distance of fertilizer K. The concentration of water-extractable K was increased in fertilizer microsites at 7 d, however, which was reduced at 28 d by the addition of HA. Co-application of HA with K decreased the concentrations of exchangeable K and non-exchangeable K as well as their movement amounts in the cinnamon soil. The results indicated that HA could decreased K fixation by soil and thus increased the availability of added K in cinnamon soil.