The invention discloses an experimental table for diagnosis of radiation EMI mechanism and a simple diagnostic method thereof. The experimental table is composed of a work table, an electric field probe and magnetic field probe group, a spectrum analyzer and a computer; the electric field probe and magnetic field probe group can take a 3D movement above the work table; the electric field probe and magnetic field probe group is alternatively connected to an input end of the spectrum analyzer, and an output end of the spectrum analyzer is connected to the computer. The diagnosis steps are as follows: dividing the plane area of the circuit to be tested into several radiated interference units; and determining radiation electric/magnetic field accurate measurement frequency range. The radiated interference units interferes the accurate measurement, regulates the scanning frequency range of the spectrum analyzer according to the radiation electric/magnetic field accurate measurement frequency range, the electric/magnetic field probes are used for measuring the level value of all the radiated interference units, and calculating the radiation electric/magnetic field intensity. The experimental table has the advantages of simple structure and low cost. By the method, the radiation EMI noise type can be rapidly and easily detected, thus providing theoretical foundation for radiation EMI noise suppression proposal.