A beam shaping assembly (60, 70) for neutron capture therapy comprising: a beam inlet (61, 71); a target (62, 72), wherein the target (62, 72) is provided to have a nuclear reaction with an incident proton beam from the beam inlet (61, 71) to produce neutrons, the neutrons forming a neutron beam, and the neutron beam moving along a main axis (X6, X7); a moderator (63, 73) adjoining to the target (62, 72), wherein the moderator (63, 73) provided to moderate the neutrons to epithermal neutron energies, wherein the moderator (63, 73) comprises at least a tapered structure; a reflector (64, 74) surrounding the moderator (63, 73), wherein the reflector (64, 74) is provided to lead the neutrons deviated from the main axis (X6, X7) back to enhance epithermal neutron beam intensity; a thermal neutron absorber (65, 75) adjoining to the moderator (63, 73), wherein the thermal neutron absorber (65, 75) is provided for absorbing thermal neutrons so as to avoid overdosing in superficial normal tissue during therapy; a radiation shield (66, 76) arranged inside the beam shaping assembly (60, 70), wherein the radiation shield (66, 76) is provided for shielding leaking neutrons and photons so as to reduce dose of the normal tissue not exposed to irradiation; and a beam outlet (67, 77); characterized in that the tapered structure comprises a main body (631, 731) and a supplement section (632, 732) surrounding the main body (631, 731); the materials of the main body (631, 731) and the supplement section (632, 732) are different, wherein the main body (631, 731) is prepared from any one of D 2 O, AIF 3, FluentalTM, CaF 2, Li 2 CO 3, MgF 2 and Al 2 O 3, and the supplement section (632, 732) is prepared from any one of Zn, Mg, Al, Ti, La, Pb, Zr, and Bi. a beam inlet (61, 71); a target (62, 72), wherein the target (62, 72) is provided to have a nuclear reaction with an incident proton beam from the beam inlet (61, 71) to produce neutrons, the neutrons forming a neutron beam, and the neutron beam moving along a main axis (X6, X7); a moderator (63, 73) adjoining to the target (62, 72), wherein the moderator (63, 73) provided to moderate the neutrons to epithermal neutron energies, wherein the moderator (63, 73) comprises at least a tapered structure; a reflector (64, 74) surrounding the moderator (63, 73), wherein the reflector (64, 74) is provided to lead the neutrons deviated from the main axis (X6, X7) back to enhance epithermal neutron beam intensity; a thermal neutron absorber (65, 75) adjoining to the moderator (63, 73), wherein the thermal neutron absorber (65, 75) is provided for absorbing thermal neutrons so as to avoid overdosing in superficial normal tissue during therapy; a radiation shield (66, 76) arranged inside the beam shaping assembly (60, 70), wherein the radiation shield (66, 76) is provided for shielding leaking neutrons and photons so as to reduce dose of the normal tissue not exposed to irradiation; and a beam outlet (67, 77); characterized in that the tapered structure comprises a main body (631, 731) and a supplement section (632, 732) surrounding the main body (631, 731); the materials of the main body (631, 731) and the supplement section (632, 732) are different, wherein the main body (631, 731) is prepared from any one of D 2 O, AIF 3, FluentalTM, CaF 2, Li 2 CO 3, MgF 2 and Al 2 O 3, and the supplement section (632, 732) is prepared from any one of Zn, Mg, Al, Ti, La, Pb, Zr, and Bi.