Abstract: A heavy water research reactor (HWRR) was designed to use natural uranium as fuel, and it has the ability to produce weapons-grade plutonium. The aim of this paper is to present the modification design scheme study of converting the HWRR to a more proliferation-resistant reactor. The neutronic and thermal-hydraulic properties of the core were calculated by CITATION+WIMSD-4, MCNP and RELAP5/MOD3.2 codes, and it was certified that the HWRR can be fueled by slightly enriched uranium instead of natural uranium. Associated the foregoing results with ORIGEN2 code calculation, it is demonstrated that the modified HWRR is less suitable for weapons-grade plutonium production, and more suitable for useful radioisotope production.