Abstract: In-hospital neutron irradiator (IHNI) is an especially designed nuclear device based on Miniature Neutron Source Reactor (MNSR) for boron neutron capture therapy (BNCT). Its rated power is 30 kW. There are a thermal neutron beam and an epithermal neutron beam for treating patients at the opposite of the core. From the thermal neutron beam, a test beam is fetched out for measurement of boron concentration in blood by prompt γ neutron activation analysis (PGNAA) method. The neutron fluence rates at the end of thermal, epithermal and test neutron beam were measured by ²³⁵U fissile target and mica slice detector. At rated power, they are 1.67×109, 2.44×10⁷ and 3.03×10⁶ cm^-2•s^-1, respectively. The results show that the thermal and epithermal neutron fluence rate can meet the requirement of BNCT and test neutron fluence rate meets the requirement of PGNAA.