Abstract: To meet the needs of experimental research, a hole must be drilled on the magnetic iron, which will affect the uniformity of the magnetic filed. A uniform magnetic field is designed and theoretical analysis of the distribution of the magnetic field is presented. The relation between boundary condition and uniformity of the magnetic field is discussed in detail and plotted into graph. Available and new experimental data are discussed on the basis of this theoretical analysis. This treatment leads to an enhanced understanding of the drilled magnetic filed.