Selective oxidation of C?H bonds under mild conditions plays an important role in the production of fine chemicals. Inspired by the active center structure and catalytic cycle of galactose oxidase (GOase), the biomimetic model compound CuL was used as a catalyst and N-Hydroxyphthalimide (NHPI) was used as a co-catalyst. Under mild conditions (O₂ 1.0 MPa, 75 °C, 6 h), the conversion of ethylbenzene was as high as 99%, and the selectivity of the oxidation product acetophenone was as high as 99%. Mechanistic studies showed that CuL forms an intermediate with NHPI, which efficiently promotes NHPI to generate PINO (phthalimide N-oxyl) radicals through electron transfer. PINO radical was used to activate C?H bonds. KIE experiment (K_NHPI-H/K_NHPI-D ≈ 3.4) indicated that the activation of NHPI was the rate-determining step. Electron paramagnetic resonance (EPR) and high-resolution mass spectrometry pointed out that the existence of alkyl radicals, peroxy radicals and hydroxyl radicals during the reaction.