Abstract: In order to calibrate the sensitivity of the scintillating-film neutron detector with the scintillator thickness great than 0.1 mm in 5SDH-2 accelerator at the Radiation Metrology Center of China Institute of Atomic Energy, a neutron shield was designed by modeling and optimizing with MCNP program. Experiment results show that this shield can attenuate the neutron fluence out of collimator to one-tenth of that in the collimator, and constrain the background signal to the level of photomultiplier’s (PMT) dark current, therefore, it can make signal to noise of the detector great than 1∶1 for the detector with thickness of scintllator above 0.1 mm. Calculation results indicate that sensitivity change resulted from collimator scattering is less than 5%.