Abstract: Constructive solid geometry (CSG) is utilized in reactor Monte Carlo code RMC, wherein all surfaces and cells are acquired to be described by users. The text format modeling is efficient and accurate but defective at poor presentation and error-proneness. Model visualization is an effective solution. An approach for model visualization, named pixel locating method, was studied in this paper. A plot module was implemented in RMC. It combined the geometry locating functions and pixel-image techniques to generate two or three dimensional graphics which display geometry or material information in CSG models. The tests were carried out using reactor models, which demonstrated the effectiveness of model visualization.