The magnetization curves and hysteresis loops of nano-cobalt ferrite samples are measured at temperatures of 5 K and 300 K. It is found that the material has large coercivity at low temperature of 5 K, and the coercivity decreases with the increase of temperature. The saturation magnetization and magnetocrystalline anisotropy constant of the material are calculated using the approaching saturation law. As the temperature increases, the thermal disturbance energy increases and the saturation magnetization decreases. The calculated results are consistent with the theoretical analysis. The magnetocrystalline anisotropy is the main factor affecting the coercive force. The calculation results show that the material has large magnetocrystalline anisotropy constant at low temperature of 5 K. With the increase of temperature, the magnetocrystalline anisotropy constant decreases rapidly, which is consistent with the trend of coercive force with temperature.