The invention discloses a back scattering radiation imaging system comprising a back scattering imaging device, a shield and a centering detection device, wherein the back scattering imaging device is used for performing back scattering radiation imaging on to-be-detected objects in a detection area; the shield is a movable structure made of a radiation shielding material, and is applicable to being arranged together with the back scattering imaging device on two sides of the detection area respectively; the centering detection device comprises a transmitting part and a receiving part which are arranged on the shield and the back scattering imaging device respectively, the transmitting part of the receiving part arranged on the back scattering imaging device is positioned nearby a position of a transmitting imaging ray bundle of the back scattering imaging device, and the transmitting part transmits a centering detection signal in a preset direction. When the receiving part receives the centering detection signal or the strength of the received centering detection signal is greater than a preset strength threshold value, a centering signal is transmitted to the back scattering imaging device. Therefore, whether the shield is installed correctly and effectively can be efficiently detected, and the safety of a radiation imaging process is improved.