A neutron capture therapy system includes an accelerator for generating a charged particle beam, a neutron generator for generating a neutron beam having neutrons after irradiation by the charged particle beam, and a beam shaping assembly for shaping the neutron beam. The beam shaping assembly includes a moderator and a reflecting assembly surrounding the moderator. The neutron generator generates the neutrons after irradiation by the charged particle beam. The moderator moderates the neutrons generated by the neutron generator to a preset energy spectrum. The reflecting assembly includes a plurality of reflectors configured to guide deflected neutrons back to the neutron beam and a supporting member to support the plurality of reflectors. A lead-antimony alloy is for the reflecting assembly to mitigate a creep effect that occurs when only a lead material is for the plurality of reflectors, thereby improving the structural strength of a beam shaping assembly.