Subnano-clusters are commonly the important active components on many catalysts in heterogeneous catalysis and finding an effective structural descriptor is key to designing new catalysts. However, the progress of obtaining such a descriptor falls far-short of expectation due to their well-known complicated structures. Herein, we propose a function of sigmoid coordination number (f(SCN)) as a structural descriptor, and develop an explicit equation to predict adsorption energies on CenO2n (n = 1-10) subnano-clusters using H adsorption as an example because of the importance of (de)hydrogenation in heterogeneous catalysis. We show an excellent linear correlation between H-adsorption energies and f(SCN) with RMSE = 0.05 eV and R2 = 0.97. The generality of this equation is also verified using other different sizes CenO2n (n = 12-14) subnano-clusters with RMSE = 0.02 eV. We demonstrate that the structural descriptor not only provides an excellent quantitative structure-reactivity relationship for metal oxide clusters, but also deepens the understanding of structure-reactivity relationship, which may have far-reaching implications in heterogeneous catalysis.