Provided is a beam diagnostic system for a neutron capture therapy system, wherein the neutron capture therapy system includes a charged particle beam, a charged particle beam inlet for passing the charged particle beam, a neutron generating unit generating a neutron beam by means of a nuclear reaction with the charged particle beam, and a beam shaping assembly for adjusting flux and quality of the neutron beam generated by the neutron generating unit and a beam outlet adjoining to the beam shaping assembly, wherein the charged particle beam inlet is accommodated into the beam shaping assembly and the neutron generating unit is accommodated in the beam shaping assembly, the beam diagnostic system includes a charged particle beam diagnostic device and a neutron beam diagnostic device, and the beam diagnostic system is used to simultaneously diagnose whether the neutron capture therapy system and/or the beam diagnostic system is malfunctioning.
