<p>The advances in flexible electronics put forward an urgent demand for ultrathin flexible heat pipes, which have high thermal conductivity and good flexibility. Aiming at the flexibility of ultrathin flexible heat pipes being limited by wicks, a two-step micro hot-pressing method was proposed for the fabrication of polymer-based ultrathin flexible microgroove wicks (UFMWs). Tungsten mold fabricated by electrical discharge machining was used in the first micro hot-pressing process and its structures were transferred to amorphous alloy molds. Amorphous alloy mold was used in the second micro hot-pressing process to fabricate UFMWs. The plasma grafting treatment was employed to modify the wettability of UFMWs. The effects of plasma grafting treatment parameters on the capillary performances of UFMWs were studied by the capillary rise tests and by analyzing the capillary performance parameters. The plasma grafting treatment successfully changed the UFMWs from superhydrophobic to hydrophilic. The minimum contact angle of the UFMWs reached 8.2°. The capillary performance parameters of UFMWs after plasma grafting treatment were 1.14–3.14 times that of the untreated UFMW. The weaker plasma grafting treatment strength may fail to generate enough rough structures and ensure sufficient grafting, which resulted in a lower capillary performance enhancement. Otherwise, the high temperature and etching effect during the plasma grafting treatment may destroy the UFMWs and reduce the capillary performance enhancement effects.</p>