Abstract: The Monte Carlo deep-penetration coupled shielding calculation method for the thermal neutron source design at Xi’an Pulsed Reactor was realized with the MCNP code. The parameters of neutron and gamma plane source at the front plane of thermal column square cavity were calculated with MCNP critical source mode and compared with the experiment value, then the correct factor for the plane source was given in this paper. Based on the neutron and gamma plane source, the thermal neutron filter was optimized with advanced borsic-aluminum material, lead, bismuth and so on. Then the upgrade scheme for the filter was introduced and the results show that the scheme can obtain high performance parallel thermal neutron beam, for which the thermal neutron flux density is increased by three times, the ratio of neutron over gamma flux density is greater than 10, and the background dose rate of neutron and gamma outside thermal beam is close to the radiation protection standard 0.025 mSv/h.