Abstract: Different thickness parts of compacted graphite cast iron(CGI)cylinder blocks were sampled from heavy truck engines.The microstructure, vermicular rate, residual stress, hardness, and tensile strength of CGI RuT450 with different casting thickness were investigated by using 3D laser microscope, scanning electron microscope (SEM), electronic universal testing machine(UTM), and X-ray stress analyzer, as well as the microstructure changes and mechanical properties of CGI RuT450 after stress relief annealing and natural aging. The results show that the graphite vermicular rate of thicker CGI castings is higher, and the compressive stress that characterizes the as-cast surface residual stress of CGI increases progressively with the increase of the sample thickness. A mild annealing treatment can remove surface residual stress more effectively than natural time efficiency on the premise of ensuring strength index.With an increase in sample thickness, the surface hardness and strength steadily reduce, and annealing treatment can further weaken the surface performance.The research offers a crucial theoretical guidance for assessing cutting performance and optimizing the cutting process of CGI.