The spin dynamics modulation has attracted extensive attention in the past decades. Rare-earth (RE) metals are essential participants in this context due to the large spin–orbit coupling. Here, with neodymium (Nd) capping, we achieve the enhancement on spin dynamic damping of Co40Fe40B20 (CFB) films by three times larger than that of CFB single layer. Based on the spin pumping theory, the interfacial spin mixing conductance Geff↑↓ is calculated as 7.3 × 1015 cm−2, which is one order larger than that of CFB/Pt. It leads to the large spin current transparency at CFB/Nd interface. By comparing of the resistivity of each layer, we found that the matched resistivity at two sides of the CFB/Nd interface plays an important role in the enhancement of Geff↑↓. As a consequence, a high spin transparency of the CFB/Nd interface is obtained as 82%. In addition, damping enhancement of CFB is not changed promptly by inserting 1–2 nm Cu layer, but it is suppressed when the Cu layer is thicker than 3 nm, which is related to the thickness dependence of the Cu resistivity. Our study broadens the horizon for the application of rare-earth (RE) in spintronics.