Co-absorbed γ-Fe2O3 magnetic powder is divided into two sorts: Co-doped γ-Fe2O3 (known as Co-γ-Fe2O3) and Co-ferrite epitaxial γ-Fe2O3 (known as CoFe-γ-Fe2O3). The coercivity of Co-absorbed γ-Fe2O3 is 100 to 400 (Oe) greater than the coercivity of γ-Fe2O3.The causes of the increasing coercivity of Co-absorbed γ-Fe2O3 were studied. The mechanism of increasing coercivity is different between the two sorts of powder: Co (OH)2 formed on the surface of γ-Fe2O3 raised its surface anisotrpy and the coercivity of Co-γ-Fe2O3 is increased. The cause of increasing coercivity of CoFe-γ-Fe2O3 is the coupling effect between the Co-ferrite epitaxial layer and γ-Fe2O3.