This study aims to reveal the changes in the microstructure of hypoeutectic gray cast iron under the addition of compositesilicon carbide powder of different mass fractions, and to explore how modified silicon carbide (SiC) particles of different sizesand contents improve the mechanical properties of hypoeutectic gray cast iron. The results showed that the modified SiCparticles increased the nucleation, the undercooling and microstructure of hypoeutectic gray cast iron, and the tensile strengthof the iron at room temperature was increased by 18,28%. The present work solves the problem that traditional SiC ceramicparticles are prone to agglomeration in molten metal, analyzes its action mechanism, and can expand the application of SiCceramic particles to strengthening metal properties of casting materials.