The present invention discloses a scanning arm and a train inspection system by imaging through radiation having the scanning arm. The train inspection system by imaging through radiation comprises a scanning arm, a detector bracket with detector arrays mounted thereon, a radiation source, a calibration device, a front collimator and a rear collimator. The scanning arm includes a rigid middle inclining section; an upper horizontal section and a lower horizontal section which are located at upper and lower ends of the rigid middle inclining section respectively and supported on a construction base; and vibration damping elements arranged between the upper horizontal section and the construction base, and between the lower horizontal section and the construction base. The detector bracket is fixedly connected with said upper horizontal section. The radiation source is suspended from the lower horizontal section by a supporting abutment. The calibration device is fixed on the horizontal ground and faces x-ray emitted from the radiation source. The front collimator is suspended from the middle inclining section, and the calibration device is located between the front collimator and the radiation source. The rear collimator is suspended from the middle inclining section, and the front collimator is located between the calibration device and the rear collimator. The sector-shaped x-ray emitted from the radiation source penetrate through the calibration device, the front collimator, the rear collimator and the train to be inspected sequentially so as to be received by the detector array provided on the detector bracket. Compared with the prior arts, the train inspection system by imaging through radiation of the present invention is advantageous in reasonable designing, good adaptation, reliable construction, stable imaging and reduced occupied area. Accordingly, the train inspection system by imaging through radiation of the present invention is advantageously applicable to inspection of trains for the customs.