The modification effect of CX-type (CX means the modifiers that have long effective term) modifiers applied in ZL108and ZL104 Al-Si alloys has been studied in detail. The results show that the morphologies of the eutectic silicon and the primary sili-con can be modified and refined simultaneously. The modification effect acts quickly and can maintain a period of 8 h by the CX-type modifiers. The CX-type modifiers increase the mechanical properties of Al-Si alloys and improve the service properties of ma-chine parts made of Al-Si alloys (such as piston and cylinder etc.). In modifying processes, the amount of the addition of CX-typemodifiers is smaller than that of any other modifiers, and the modifying procedures are simple. There are no smoke, no dust, and noirritant smell in modifying processes using CX-type modifiers. Therefore, the CX-type modifiers have advantages in economy andenvironment protection.