Single-atom catalysis of isomorphous substituted bimetallic oxide TMV 3 O 10 (TM=Sc, Ti, Cr and Co) is explored by spin–polarized density functional theory calculations. The single atom substitution in V 4 O 10 does not make significant change to the geometric or electronic structures of the cluster; while it brings specific and tunable catalytic activity depending on the TM substituent. The d-projected density of state near the Fermi level is found to play important roles in the catalytic performance of single-atom catalysts. Our findings reveal the structural basis of the activity of bimetallic oxide clusters and shed some lights on the catalytic mechanism of single-atom catalysis.