Abstract: With the continuous improvement of train speeds, the influence of aerodynamics on the train safety is increasingly prominent. Especially, the crosswind will significantly deteriorate the aerodynamic performance of high-speed trains and bring greater security risks consequently. Present research regarding the crosswind effect on high-speed trains usually assumes that the train surface is smooth, which is, however, not true. Non-smooth surfaces with microstructures will change the flow characteristics in the boundary layer and may improve the aerodynamic performance of high-speed trains. The present study uses an improved delayed detached eddy simulation (IDDES) method was used to obtain the aerodynamic performance of 1∶25 scale train models with smooth and rough surfaces under crosswind. The non-smooth surface is achieved by adding a group of rectangular strips on the top of the train model. The results show that the side force coefficient and the roll moment coefficient can be respectively reduced by 3.71% and 10.56% by using a non-smooth surface. The width, height, and length of the strip are selected as design variables, and different numerical simulation schemes are designed based on the orthogonal experimental design method. The relationship between the geometric parameters of rectangular strip and the side force coefficient and roll moment coefficient of the train is explored by the variance and range analyses, and the optimized strip shape is given. This study can hopefully provide a theoretical basis for the improvement of aerodynamic performance of high-speed trains under crosswind.