Abstract: In order to investigate the railcar flow operation optimization of heavy haul transportation loading side, the railcar organization process in the strategic loading domain of heavy haul transportation was analyzed. According to the supply level of goods resource and transportation operation mode, the stations in the strategic loading area were classified into three levels, including strategic loading point, strategic loading area, and strategic loading domain. Then, a railcar flow combination scheme optimization model was established, which is based on the characteristics that car flows are organized in the way of unit heavy haul train and combined heavy haul train. In this model, minimization of the total combined time of the combined heavy haul train was the objective, the yearly target traffic volume, line capacity, loading capacity of loading point (area), etc. were constraints, and combination mapping was adopted to deal with the railcar flow delivery relationship in the combination station. In addition, an effective heuristic method was designed to solve the model. The results of a case study show that three equivalent combination schemes can be obtained by the proposed optimization method. Among them, optimization scheme 2 is consistent with the real railcar flow organization scheme, and the other two equivalent schemes, although with different combination contents, have the same time consumption.