A system to test efficacy of electromagnetic shielding includes a radio frequency anechoic housing and a testing device. The testing device includes a signal source, at least one antenna, and a receiver. When one of the antenna is connected to the signal source, the receiver receives a first frequency field. When the antenna and the signal source are in the shielding shell and the shielding shell is in the radio frequency anechoic housing, the receiver receives a second frequency field. Values of the shielding efficacy are obtained according to the first frequency field and the second frequency field. A determination of whether the shielding shell meets requirements is obtained according to the values of the shielding efficacy. A method for testing shielding efficacy is also disclosed.