Abstract: The effect of shrinkage porosity on the mechanical properties of QT400-18L nodular cast iron was studied by means of static tensile test, low temperature impact test, Brinell hardness test and microstructure analysis. The results showed that shrinkage porosity made strength and ductility decrease significantly; the type of fracture was mainly ductile fracture; impact fracture was composed of a large number of cleavage and a small amount of dimples; Brinell hardness lower than the standard hardness at least 9%; but shrinkage porosity had little effect on graphite morphology, distribution and microstructure of the material.