The invention relates to a casting high-chromium alloy modeling method based on molecular dynamics and belongs to the field of alloy material structural design. According to the modeling method, modeling of a composition structure of casting high-chromium alloy is conducted through molecular dynamic modeling software, firstly, characteristic parameters of the casting high-chromium alloy, an atomic model of a construction body-centered cubic crystal structure and an atomic model of a construction face-centered cubic crystal structure are obtained; then, by means of a substitution program, existing atoms in the models are substituted with the chromium atoms; the content of the substitution element is judged, and if the content requirement is not met, substitution continues till the chromium element meets the requirement in the alloy; finally, by means of the Voronoi algorithm, the constructed models are optimized till the content requirement of all elements in the alloy is met. The modeling method can accurately reflect microstructure components and the structure of the alloy, and has practical significance to property and machining method research of alloy.