The error distribution between Miedema-calculated values and reference-reported values for formation enthalpies of binary Al-RE intermetallics was analyzed and it is known that the calculated results are commonly negative compared with those in references. Therefore, an important influencing factor, radius ratio of RE atom to aluminum atom should be considered to modify the thermodynamic calculation model in the study. The calculation results of the modified model are more closed to the reported experiment results and the error was found to be reduced from 33.6% to 5%. The enthalpies of some common intermetallics of aluminum and rare earth were also checked by MTDATA for comparison. All that proved the modified calculating model are much more accurate and reliable. The common formation enthalpies of intermetallics of aluminum and rare earth as well as Al-Er, Al-Tb, Al-Gd, which are studied less, are calculated by the modified Miedema model.