The composition range of amorphous forming for Al-Fe-Zr system has been determined by mechanical alloying of mixture of elemental powders．The phases of as-milled powders were analyzed by XRD．The composition range of amorphous forming of Al-Fe-Zr was also predicted from the thermodynamic point of view．In the procedure of prediction，the effects on the formation enthalpy of substitution or interstitial position of solute atoms are included．The agreement between the prediction and experiments is reasonable．The reasons of discrepanc between the theory and experiment are discussed．