Abstract: Aiming at the lack of reusability and portability in the manual optimization of software, we propose and implement SEMD, a cross-platform automatic performance optimization programming tool for numerical simulation software. It abstracts numerical computing loop programming using high-level semantics, which is prevalent in the field of numerical simulation, completely shielding underlying hardware features and performance optimization implementations. Therefore, any numerical subroutines written based on SEMD can attain automatic cross-platform performance portability. Our tests demonstrate that SEMD's performance optimization effects exceed those of comparable products on three different processor architectures, including X86, ARM and GPU. Furthermore, SEMD has been successfully applied in the development of four real numerical simulation software programs in the fields of structure, fluid, and electromagnetic, resulting in an average performance improvement of 164% on hotspot subroutines.