Carbon‐supported single atomic metals (SAMs) have attracted great interest in energy research. However, it is still a great challenge to control the content of SAMs in carbon. In this work, a dynamic inhibition strategy is proposed to achieve content‐controllable synthesis of Cu atoms loaded in carbon nanofibers (CNFs) using polyacrylonitrile (PAN) and Cu(NO₃)₂ as precursors by electrospinning. Interestingly, N‐anchoring sites in PAN‐derived carbon matrix are dynamically increased to inhibit the aggregation of Cu atoms. Therefore, Cu atom content can be linearly controlled by adjusting the ratio of Cu(NO₃)₂/PAN, and a high mass content of 8.57 wt% can be achieved despite a low surface area of only 10 m² g⁻¹ for Cu‐doped CNFs. Atomic Cu is stabilized by N to form CuN₃ coordination. More interestingly, N‐coordinated Cu atoms can not only improve the lithium‐ion diffusion kinetics in the CNFs, but also act as reversible Li storage sites. Therefore, Cu‐doped CNFs exhibit excellent rate and cycling performance for Li‐ion storage. Moreover, lithium‐ion capacitors, assembled by Cu‐doped CNFs as anode materials, can deliver high energy density (183.2 Wh kg⁻¹) and high power density (11.0 kW kg⁻¹). This concept opens up unique horizons for the design of SAMs toward new applications in energy storage.