The ability of outdoor power distribution equipment to protect against the Lightning Electromagnetic Pulse(LEMP) is studied by XFDTD full wave 3D electromagnetic field simulation software based on Finite Difference Time Domain(FDTD) method, including simulating the coupling of the near-field lightning electromagnetic pulse with the cabinet of outdoor box-type substation, which is characterized with slots. The coupling electric field strength and the electromagnetic power density of the three types of substations with different shapes of aperture array are obtained at 30 m from the return point, and at 5 cm, 50 cm and 100 cm from the opening position. It is concluded that when the LEMP whose energy is mainly concentrated on the low frequency band(below 2 MHz) couples on the anterior aperture array, the coupled electric field energy in the substation is mainly focused near the opening. The electromagnetic energy coupling into the substation with rectangular, square and circular aperture arrays decreases in turn, and the substation with circular aperture array has optimum shielding effectiveness. The electromagnetic hazard in the cavity far away from the aperture array is less than that near the opening position. The coupled electromagnetic energy will have impacts on the normal operation of the substation, but will not damage its internal electronic components.