Abstract: This paper proposes a conceptual design for an innovative reactor, reduced moderation small modular reactor (RMSMR), based on the technology of conventional PWRs. In this paper we firstly establish a two-dimensional model to analyze the influences of fuel types, coolant types and other parameters of PWR and RMSMR. Then a three-dimensional design scheme is proposed and a preliminary neutronic and thermal-hydraulic analysis is carried out. The results show that the power distribution can be flattened by adopting a three-zone 232Th-233U dioxide fuel configuration, a negative void coefficient can be ensured by using uranium-thorium dioxide fuel, and the conversion effect can be enhanced by utilizing blanket regions. RMSMR utilizes the small scattering cross section of heavy water to yield an epithermal-to-fast neutron spectrum, which is also beneficial for attaining a large conversion ratio, a long core lifetime and reducing the burnup reactivity swing. It is concluded that RMSMR can sustain the power generation of 100 MWe for 6 years without refueling, which is of referential value to the design of new generation reactors.