The present invention discloses a scanning device of back-scatter imaging with a radiation beam, comprising: a radiation source; a fixed shield plate and a rotatable shield body disposed between the radiation source and a object to be scanned respectively, wherein the fixed shield plate is stationary with respect to the radiation source and the rotatable shield body is rotatable with respect to the fixed shield plate. The fixed shield plate is provided with a ray passing-through region thereon, which allows for a radiation beam from the radiation source to pass through the fixed shield plate, a ray incidence region and a ray emergence region are arranged on the rotatable shield body respectively, during the rotatable scanning of the rotatable shield body, the ray passing-through region of the fixed shield plate continuously intersects with the ray incidence region and the ray emergence region of the rotatable shield body to generate collimated holes for scanning. The ray passing-through region of the fixed shield plate is a rectilinear slit, the rotatable shield body is a cylinder, and the ray incidence and emergence regions are configured to be a series of small discrete holes disposed along a spiral line respectively. In addition, the present invention discloses a scanning method for back-scatter imaging with a radiation beam.