Segmented metal–metal heterostructure nanorods/nanowires are very promising for development in photoelectric devices, wearable electronics, biomedicine, and energy storage due to unique surface and interface and adjustable electronic and optical properties. Regretfully, most of the segmented heterojunctions are presently synthesized in organic solvent, and its electronic dynamics is still rarely studied and poorly understood. Here, we reported a pressure-assisted one-step aqueous-phase strategy to successfully synthesize segmented Ag–Au–Ag heterojunction nanorods (HJNRs), the aspect ratios and heterojunction contents of which can be well controlled by varying pressure value. The heterojunction-induced femtosecond-to-nanosecond dynamics in 1D direction of the Ag–Au–Ag HJNRs were for the first time acquired and presented a unique regularity tendency (e.g., electron–phonon scattering time). The unprecedented aqueous-phase strategy opens up horizons of synthesis of other segmented metal–metal HJNRs, and the fascinating Ag–Au–Ag HJNRs are hopeful for the development of a new class devices in photothermal and photoelectronic fields.