In order to study the electrostatic discharge（ESD） process and its radiation field distribution deeply

and to solve the bad repeatability of measurement data and the difficulty of near field observation and measurement

we estalished an ESD 3 D electromagnetic model and verified the model by the combination of electromagnetic simulation and experiment.Moreover

we analyzed the characteristics of the radiation field of the horizontal coupling plate and the coupling voltage characteristics of equipment under test（EUT）.The study reveals that the radiation field of the horizontal coupling plate has the maximum electric field intensity at the discharge point

and the field strength decreases with the increase of the distance from the discharge point.Besides

the results of 3 D electromagnetic simulation show that the ESD radiation field is mainly coupled to the inside of the device through the gap and interface of the EUT shell.The coupling voltage is consistent with the test results.Therefore

in the design stage of electronic equipment

the 3-dimensional electromagnetic model can be used to verify its internal immunity

which helps to reduce research cost and improve pass rate of ESD immunity test.