Catalytic ozonation is progressively becoming an attractive technique for quick water purification but efficient and stable catalysts remains elusive. Here we solvothermally synthesized highly-dispersed Co_3O_4 nanocrystals over microscale nitrogen-doping graphene(NG) nanosheets and tested it as a synthetic catalyst in the ozonation of phenol in aqueous solutions. Transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy were used to determine its morphology, crystallinity, elemental composition and molecular bonds, respectively.The comparative experiments confirmed the highest catalytic activity and oxidation degree(AOSC) of Co_3O_4/NG among four nanocomposites(G, NG, Co_3O_4/G, and Co_3O_4/NG). Co_3O_4/NG also has exhibited the highest degradation rate: complete conversion of a near-saturated concentration of phenol(941.1 mg/L) was achieved within 30 min under ambient conditions with only a small dosage of Co_3O_4/NG(50 mg/L) and ozone(4 mg/L, flow rate:0.5 L/min). It also resulted in 34.6% chemical oxygen demand(COD_(Cr)) and 24.2% total organic carbon(TOC) reduction. In this work, graphene nanosheets not only functioned as a support for Co_3O_4 nanocrystals but also functioned as a co-catalyst for the enhancement in phenol removal efficiency. The surface nitridation and Co_3O_4 modification treatment further improved the removal rate of the phenol pollutants and brought in the higher oxidation degree. Our finding may open new perspectives for pursuing exceptional activity for catalytic ozonation reaction. Catalytic ozonation is progressively becoming an attractive technique for quick water purification but efficient and stable catalysts remains elusive. Here we solvothermally synthesized synthesized highly-dispersed Co_3O_4 nanocrystals over microscale nitrogen-doping graphene (NG) nanosheets and tested it as a synthetic catalyst in the ozonation of phenol in aqueous solutions. Transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy were used to determine its morphology, crystallinity, elemental composition and molecular bonds, respectively. (AOSC) of Co_3O_4 / NG among four nanocomposites (G, NG, Co_3O_4 / G, and Co_3O_4 / NG). Co_3O_4 / NG also has the highest degradation rate: complete conversion of a near-saturated concentration of phenol ( 941.1 mg / L) was achieved within 30 min under ambient conditions with only a small dosage of Co_3 It also resulted in 34.6% chemical oxygen demand (COD Cr) and 24.2% total organic carbon (TOC) reduction. In this work, graphene nanosheets not only function as a support for Co_3O_4 nanocrystals but also functioned as a co-catalyst for the enhancement in phenol removal efficiency. The surface nitridation and Co_3O_4 modification treatment further improved the removal rate of the phenol pollutants and brought in the higher oxidation degree. Our finding may open new perspectives for pursuing exceptional activity for catalytic ozonation reaction.