Recycling nickel slag by aluminum dross can realize the ‘utilization of waste heat’ and the ‘recovery of waste into resource’. Based on the molecular dynamics study, the influences of w(‘FeO’)/w(Al2O3) and w(Al2O3)/w(SiO2) on the degree of polymerization (DOP) evolution have been discussed. As w(‘FeO’)/w(Al2O3) decreases from 1.69 to 0.48, the first peak of the Si-O pair in radial distribution functions (RDFs) shifts from 1.65 to a lower abscissa value of 1.63, and the mean square displacement (MSD) distributions of both Ca and Si atoms decrease. Similarly, w(Al2O3)/w(SiO2) induces a higher slag DOP. Under different w(‘FeO’)/w(Al2O3) and w(Al2O3)/w(SiO2), DCa, DFe, DO, DA1 and DSi of each atom are between 7.74∼12.80 × 10−11, 6.08∼11.78 × 10−11, 2.88∼9.56 × 10−11, 2.05∼3.78 × 10−11 and 1.58∼3.37 × 10−11 m2 s−1, respectively. The increasing predicted viscosities keep a good accordance with the experimental data, signifying the increasing DOP of slags from the macro level.