The preparation of noble metal‐free catalysts for water splitting is the key to low‐cost, sustainable hydrogen generation. Herein, through a pyrolysis‐oxidation process, we prepared a series of Co‐Fe‐Ni trimetallic oxidized carbon nanocubes (Co1‐XFeXNi‐OCNC) with a continuously changeable Co/Fe ratio (X=0, 0.1, 0.2, 0.5, 0.8, 0.9, 1). The Co1‐XFeXNi‐OCNC shows a volcano‐type oxygen evolution reaction (OER) activity. The optimized Co0.1Fe0.9Ni‐OCNC achieves a low overpotential of 268 mV at 10 mA cm−2 with a very low Tafel slope of 48 mV dec−1 in 1 m KOH. At the same time, the stability of the Co0.1Fe0.9Ni‐OCNC is also outstanding; after 1000 CV cycles, the LSV plot is almost coincident. Moreover, the potential remains almost of the same value at 10 mA cm−2 after 12 h in comparison to the initial value. The excellent electrocatalytic properties can be attributed to the synergistic cooperation between each component. Therefore, the Co0.1Fe0.9Ni‐OCNC is a promising candidate instead of precious metal‐based electrocatalysts for OER.