We performed 200ns all-atom molecular dynamics simulation for WT, Delta and Omicron variant RBD-ACE2 complex in triplicate and the mean value of three repetitions for each measurement was used for analysis. According to the predicted binding free energy (Table ), the ΔGs of ACE2-RBDDelta in three repeating experiments are all about 10 kcal/mol higher than that of ACE2-RBDWT. The average number of ΔG of RBDDelta to ACE2 (-42.76 ± 2.38 kcal/mol) demonstrated stronger binding than that of that of RBDWT (-33.13 ± 3.26 kcal/mol). The result is in good agreement with existing experimental findings, proving that our method is reliable to a certain extent . By contrast, the difference of ΔG between ACE2-RBDOmicron and ACE2-RBDWT is only 3.74 kcal/mol (Table ), suggesting that although there are a high number of mutations in S protein RBD, they don't increase affinity to ACE2 and even slightly weaken the binding.