Abstract: Using different carbon equivalent contents, the chemical compositions of gray cast iron material used for an engine were improved and optimized with the ratio of silicon content to carbon content (cSi/cC) changing from 0.63 (before improvement) to 0.7 (after improvement), and the static mechanical properties and fatigue properties of the attached cast test blocks were tested before and after improvement. The results show that when the carbon equivalent content cCE=3.80% (mass) and cSi/cC=0.7, the performances of the gray cast iron material were in good condition. The material with higher cSi/cC had higher elastic modulus, and the tensile strength and total extension proof strength also increased with the increase of elastic modulus. Under the same fatigue condition, the material with higher elastic modulus had higher fatigue cycles. After improvement, the tensile strength of the gray cast iron material was 330~350 MPa, the elastic modulus was 185 000~195 000 MPa, and the tensile fatigue limit was 47.5~51 MPa.