In order to improve flux and quality of neutron sources, the disclosure provides a beam shaping assembly for neutron capture therapy includes: a beam inlet； a target, wherein the target has nuclear reaction with an incident proton beam from the beam inlet to produce neutrons； a moderator adjoining to the target, wherein the neutrons are moderated by the moderator to epithermal neutron energies, the moderator includes a main body and a supplement section surrounding the main body, the main body and the supplement section form at least a tapered structure； a reflector surrounding the moderator； a thermal neutron absorber adjoining to the moderator； a radiation shield arranged inside the beam shaping assembly, wherein the radiation shield is used for shielding leaking neutrons and photons so as to reduce dose of the normal tissue not exposed to irradiation； and a beam outlet.
