Electromagnetism signal correlation interferometer is the updating product of the old type electromagnetism overcast interferometer. In order to interfere the signals including secret information (that) the computer with secret information sends out via electromagnetic waves the interferometer takes use of numeric sequence synthesize technique to produces random signals and video frequency positive order scanning interference technique to produces numeric interference signals and noise mixture technique to interfere and overcast signals. The various interference signals' multiplex function can enhance the protective effects of the electromagnetism interference signals, which make it even hard or impossible for the thief to steal secret information. Since this product is provided with low radiation power and better electromagnetism compatibility that the effective time to interfere radiation is shorten and the radiation influence to human is reduced. This is also provided with such virtue as small cubage , beautiful outline and easy installation.