Abstract: In order to complete the miniaturization of medium-voltage electrical penetrations and evaluate the equipment status of penetrations under short-circuit conditions, the electromagnetic numerical calculation model of two groups of three-phase medium-voltage electric penetration assemblies was established by using the FEM. Based on the model, the electromagnetic field distribution of the electrical penetration and the transient change process of the electrical stress of the conductor when a group of conductors are short-circuited are calculated and analyzed. Through the comparison and analysis with the calculation results of the formula, it can be seen that the model established in this paper can accurately calculate the electromagnetic force transient change process of the medium piezoelectric permeable component under the short-circuit condition, and can accurately evaluate the operating state of the equipment. Based on the above model calculations, the relationship between the short-circuit electric stress peak value and the initial phase angle, the effective value of the short-circuit current and the radius of the conductor distribution circle is discussed, and it is known that when the penetration is in the short-circuit test, the appropriate initial phase angle should be selected to increase the test severity and reasonably test the equipment performance. And when the rated current carrying capacity of the medium voltage electrical penetrating parts is small, the arrangement of two groups of three phases can also be adopted. The results of this study can be used in the structural optimization design of the medium-voltage electric penetration assemblies and the mechanical strength checking.