Abstract: To reduce the load on industrial plant roofs in photovoltaic projects and enhance safety, the paper proposes a lightweight design scheme for photovoltaic supports based on material upgrading. By using S550 high-strength steel with a wall thickness of 1.5 mm to replace the traditional 2.0 mm thick Q235B steel used in purlins, significant weight reduction of the supports is achieved. Three methods—YJK software, PKPM Toolbox, and ABAQUS finite element simulation software are employed to compare and verify the deflection of the purlins. The results show that after adopting thin-walled S550 steel, the maximum deflection of the purlins is only 1/285 of their length, outperforming the standard requirement of 1/250. Through material upgrading, the weight of the purlins is reduced by approximately 24%, and the overall weight of the support structure decreased by 12%. Furthermore, the comprehensive cost of the photovoltaic supports is reduced by approximately 13%. This lightweight design scheme provides an effective and cost-efficient solution for industrial plant roof photovoltaic projects, offering valuable insights and references for similar applications.