Abstract: Fe−6.5%Si (mass fraction) powders were subjected to the heat treatment experiments at the different temperatures combined with the heat treatment of the magnetic powder cores. The effect of heat treatment on the magnetic properties of Fe−6.5%Si magnetic powder cores, such as permeability and loss, was investigated. In the results, the powder heat treatment can greatly eliminate the defects caused by the impact of high pressure gas on the alloy powders during the gas atomization powder production and reduce the carbon and oxygen content in the powders. With the increase of heat treatment temperature, the coercive force of the powders first increases and then decreases, and the saturation magnetization gradually decreases. The magnetic properties of the prepared Fe−6.5%Si magnetic powder cores can also be improved by heat treatment. After the heat treatment at different temperatures, the loss is maintained between 600 and 700 mW∙cm⁻³, and the lowest value is 625 mW∙cm⁻³. Compared with other comparison samples, the magnetic powder cores made of the Fe−6.5%Si powders heat-treated at 900 ℃ have the better magnetic conductivity and loss after the subsequent heat treatment at 800 ℃.