In recent years, more and more attention has been paid to the refinement and authenticity of models in nuclear reactor design and safety analysis. In the numerical simulation of the reactor, both neutron and thermal-hydraulics have a great influence on the calculation results. At the same time, because the neutron energy spectrum and the power distribution of the reactor strongly depend on the thermal-hydraulic properties of the coolant, neutronic and thermal-hydraulic coupling (N/TH) allows for a more precise analysis of the reactor. In this paper, based on the Picard method, a set of implicit and high-precision neutronic and thermal-hydraulic coupling codes is developed, which connects the Monte Carlo code RMC (Reactor Monte Carlo code) and the computational fluid dynamics code STAR-CCM+, processes the files and data generated during the coupling process, and transfers them to thermal-hydraulic and neutron simulation. The accuracy and reliability of the coupling code developed in this paper are verified by comparing it with the calculation results of the single rod model of the University of Illinois at Urbana-Champaign (UIUC). In this paper, a conceptual design of a lead-bismuth-cooled solid reactor is proposed, and an optimal design is obtained through the multidimensional and full-scale optimization of the reactor. Then the coupling code developed in this paper is used for coupling simulation to study its neutron and thermal-hydraulic properties under various transient conditions.