Abstract: The average volume of the magnetic Barkhausen jump (AVMBJ)is generated by the irreversible displacement of the magnetic domain wall under the effect of the excited magnetic field on ferromagnetic materials. The effects of excited magnetic field and temperature on AVMBJ are studied in this paper. Firstly, according to ferromagnetism, the numerical relationships of irreversible magnetic permeability and reversible magnetic permeability are derived so that the mathematical expression of AVMBJ is simplified by that relationships. Secondly, the functional relationship between saturation magnetization and temperature is employed in this paper to deduce the explicit mathematical expression among AVMBJ, temperature, excited magnetic field by the ferromagnetic “molecular field” theory. Finally, the AVMBJs are measured under different temperatures and different excited magnetic fields to verify our theories.