Magnesium-based materials are favored by researchers because of their high hydrogen storage capacity, but they cannot be put to daily use because of their more demanding reaction conditions. Recently, the method to improve the hydrogen storage performance of MgH2 by catalyst doping has been widely investigated. In this paper, Co3O4 catalysts were prepared by homogeneous precipitation method. It was demonstrated that the Co3O4 catalyst could effectively improve the hydrogen storage performance of MgH2. According to the experimental results, the dehydrogenation onset temperature of the MgH2+15 wt% Co3O4 composite was about 200 °C, which was about 130 °C lower than that of pure MgH2, and the amount of dehydrogenation was 6.26 wt%. The dehydrogenation activation energy of the MgH2+15 wt% Co3O4 composite was reduced to 89.13 kJ/mol, which was about 45.7% lower than that of pure MgH2. After complete dehydrogenation, the composites started to absorb hydrogen at 50 °C with 6.2 wt%, while the activation energy of reabsorption was also reduced to 47.97 kJ/mol. After 10 cycles of MgH2+15 wt% Co3O4 composites, the hydrogen storage capacity of MgH2 could still be maintained at 99%, which indicated that it had good cycling stability. It was confirmed by various characterizations that Co3O4 was uniformly distributed on the MgH2 matrix after ball milling. After the first reaction, Co3O4 was converted to CoO, which was uniformly attached to the Mg/MgH2 surface and stabilized during the cycling process, continuing to provide active sites for hydrogen. The hydrogen storage composite MgH2+Co3O4 was prepared in this study, and Co3O4 was uniformly distributed on the MgH2 matrix. In the first hydrogen release process, Co3O4 is gradually converted to CoO, and then in the hydrogen absorption process, hydrogen enters Mg. During the cycle, the CoO is in a stable state and evenly dispersed on the Mg/MgH2 surface, continuing to provide an active site for hydrogen. Display omitted •Co3O4 with good air adaptation performance is applied to MgH2 system.•Composites started to release H2 at 200 °C and could start to absorb H2 at 50 °C.•The activation energy of de/hydrogenation was significantly reduced for composites.