The chitosan oligosaccharide derivative BHC as a green corrosion inhibitor for corrosion inhibition was synthesized using natural macromolecular chitosan oligosaccharide, glycidyltrimethylammonium chloride and benzaldehyde as raw materials. The corrosion inhibitor BHC was characterized by FTIR and 1HNMR. The inhibition performance and mechanism of BHC were evaluated by weight loss method, electrochemical analysis, scanning electron microscope (SEM), atomic force microscopy (AFM) and contact angle measurement. The results showed that the optimized synthesis conditions of BHC were obtained as follows：m(HTCOS): m(benzaldehyde)=1:2.4，reaction temperature 80℃ and reaction time 24 h. When the total pressure was 15 MPa (the partial pressures of H2S, CO2 and N2 were 1 MPa, 5 MPa and 9 MPa, respectively), the corrosion inhibition rate of BHC (100 mg/L) on P110 steel corrosion at 140℃ in H2S/CO2 corrosive medium was 85.62%, 16.9% higher than that of commercial corrosion inhibitors corrosion inhibitors, which can effectively reduce the corrosion rate of P110 steel under high temperature and high H2S/CO2 corrosion environment. Corrosion inhibitor BHC was a mixed type corrosion inhibitor with predominant control of cathodic reaction. The adsorption of BHC on the P110 steel surface obeyed the Langmuir adsorption isotherm. And it formed a stable covalent bond with the steel surface, which can well protect the steel pipe.