Polyoxometalates (POMs) are known for their well-established catalytic properties, particularly in photocatalysis, and have made significant strides in achieving selective C(sp³)−H functionalization. However, due to the complexity of the POM structures, the reactivity and regioselectivity of POMs in organic conversions remain unclear. Here, the reactivity and regioselectivity of the C(sp³)–H trifluoromethylation of pyrrolidine via decatungstate anion/copper ([W₁₀O₃₂]⁴⁻/Cu) dual catalysis were theoretically investigated. Density functional theory (DFT) computations revealed that the β-regioselective activation of pyrrolidine occurs more readily than does α-regioselective activation; this is due to the reduction in activity of the ortho α-C–H bond by protonation. Furthermore, the reactivity of hydrogen atom transfer (HAT) catalysts for C(sp³)–H bond activation follows the order [W₁₀O₃₂]⁴⁻ > amine radical cation > fluorescein. The outstanding reactivity of [W₁₀O₃₂]⁴⁻ is attributable to its rigid structure and exposed active surface sites. We demonstrate a linear relationship between the steric volume of the protective group on pyrrolidine and the C–H bond selectivity catalyzed by [W₁₀O₃₂]⁴⁻. In other words, a larger steric volume of the protective group on pyrrolidine leads to easier attainment of a single C_β–H bond activation product. We hope that this theoretical analysis will provide valuable guidance for obtaining high selectivity target products in experimental setups.