The present disclosure provides a positioning assembly for a radiation irradiation system. The positioning assembly includes a shielding body made of polymer and radiation shielding material capable of shielding the radiation and a sealing bag for accommodating the shielding body, when the target to be irradiated is placed on the positioning assembly, the positioning assembly is recessed with a shape of the target at the position where the target is placed and forms a contour corresponding to the target to position the target to be irradiated.
