The (Cu42Zr42Al8Ag8) 100-xSix amorphous alloy rods, x =U to 1, with i mm in diameter were prepared by Cu-mold drop casting method. The glass forming ability, thermal properties and microstructure evolution was studied by differential scanning calorimetry (DSC), and X-ray diffractometry (XRD). The XRD result reveals that these as-quenched (Cu42Zr42Al 8Ag8)100-xSix alloy rods exhibit a broaden diffraction pattern of amorphous phase. The crystallization temperature and GFA (glass forming ability) of (Cu42Zr42Al 8Ag8)100-xSix alloys increase with the silicon additions. The highest Trg (0.59) and y value (0.405) occurred at the (Cu42Zr42Al8Ag 8)99.75Si0.25 and (Cu42Zr 42Al8Ag8)99.75Si0.25 alloy. In addition, both of the activation energy of crystallization and the incubation time of isothermal annealing for these (Cu42Zr 42Al8Ag8)100-xSix alloys indicates that the (Cu42Zr42Al8Ag 8)99.25Si0.75 alloy posses the best thermal stability among the (Cu42Zr42Al8Ag 8)100-xSix alloy system.