For forming the metallic magnetic powder of magnetic recording medium magnetism layer, sacrifices magnetism characteristic if for improving the oxidation resistance to form the oxide film on the surface of the thick particle. The invention is concerned with the magnetic recording medium magnetic powder that composing of the acicular particle with irons mainly, the characteristic is: the particle includes the Co with the range that the Co/Fe is under 50at.%, the Co/Fe testing by the XPS is with higher value comparing with the surface part and the core part of the particle, the particle presents two oxidation start-point of the low-temperature side oxidation start-point and high-temperature side oxidation start-point when it is for the TG test.