As a new generation of metal‐free carbon catalyst, the sp3@sp2‐hybridized bucky nanodiamond (ND) is competitive even compared to the traditional metal catalysts in many oxidative reactions. However, the application of the carbon catalyst in reduction reaction is barely conducted and the mechanism of this kind of reaction is generally unknown. To develop a wider scope of carbon catalysts and achieve an industrial promising activity of the metal‐free catalyst, here a series of sp3@sp2‐hybridized bucky ND for catalyzing a model reduction reaction of 4‐nitrophenol to 4‐aminophenol is developed, in which a quite satisfying metal‐free catalytic performance (better than many metal catalysts) is obtained and the discipline of getting better activities for the reduction reaction is revealed. The oxygen functionality and sp3/sp2 hybridized carbon ratio are confirmed to be the important influential factors. The similarity of the carbon catalyzing the reduction and oxidation reactions might bring a uniform concept for redox reactions with carbon catalysts.

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