Abstract: Thermal neutron radiography is a powerful nondestructive detecting technique as an important complement to X-ray radiography. The miniaturized thermal neutron radiography system holds great potential in research and industrial applications. Based on the compact D-D neutron generator, a neutron moderator-collimator for thermal neutron radiography was designed and simulated by using Monte Carlo N-Particle Transport Code(MCNP-4C) to track neutrons and γ-rays. The aspect ratio of the moderator-collimator was about 3.58. The simulation results showed that the thermal neutron flux rate could reach and exceed 10³ n/(cm² · s) in the sample plane when the neutron yield of D-D neutron generator is greater than 5×10⁸ n/s. The proportion of thermal neutron in the collimated neutron beam was found to be over 74%. In a irradiation field with a diameter of 70 mm, the non-uniformity of thermal neutron flux was kept at 7.3%, which meets the imaging criteria of thermal neutron radiography.