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• A parametric design approach of composite external shading system for classroom is proposed. • The structural dimensions of the integrated external shading boards are obtained. • The structural dimensions of the perforated shading panel are obtained. • The optimal composite external shading system has good lighting and energy performance. • The approach is suited for designing a composite external shading system for the classroom. Energy consumption and visual comfort are issues worthy of concerning in the teaching buildings. To improve the light and thermal environment in the classroom, structural dimension parameters of shading system are optimized by the multi-objective genetic algorithm based on the lighting, energy consumption, and visual comfort in this study. The 3D parametric modeling of the classroom is performed by using the Grasshopper and Rhino software, and the quantitative impact of the integrated external sunshade and perforated external shading panel on the lighting, air conditioning and heating energy consumption, and visual comfort of the classroom are analyzed by the Radiance, Daysim, and EnergyPlus calculation engines. Subsequently, the optimal structural dimensions of the composite shading system in the east, west, south, and north orientations in Nanchang area are determined. The optimized results show that the optimal dimensions (width of the vertical shading board W; overhang length of the horizontal shading board L) of the integrated external shading boards in the east, west, south, and north orientations for the established classroom model are (0.3; 1.8), (0.6; 1.2), (0.4; 0.8), and (0.5; 0.7), respectively, as well as the optimal structural dimensions of the perforated shading panels (perforated panel to window ratio – perforation percentage – holes arrangement) are 71.5%–30%–crossing arrangement, 70%–50%–crossing arrangement, 90%–30%–crossing arrangement, and 65.6%–70%–matrix arrangement, respectively. It is found that total annual energy use intensity is reduced by 4.5% to 18.8%, the lighting quality in the near-window region (region I) is improved by 25% to 37%, the visual comfort in the classroom is improved by more than 30%, and the solar irradiance of the window is reduced by at least 27%. The proposed design approach of the classroom external shading system can not only greatly improve indoor lighting quality and visual comfort but also reduce total annual energy use intensity. [ABSTRACT FROM AUTHOR]