One kind of gray graphite cast iron for fabricating cartridge value was studied. Their mechanical properties and microstructure were analyzed by OM,SEM,EDS. The results show that graphite length is about 144.6 μm (Degree 8). The volume of cementite is lower than 3% (Degree 3). And the matrix is made of ferrite and pearlite. The phosphide eutectic in gray graphite cast iron has a large influence on its mechanical properties. 