Abstract: Abstract: As an ideal clean energy, biomass is friendly to the environment. Bio-oil is a brown and black viscous liquid obtained by rapid pyrolysis of biomass under anoxic conditions. As a kind of liquid fuel, it has the disadvantages of high acid value, high water content, high viscosity and low calorific value. In addition, bio-oil is the mixture of hundreds of chemicals. Carboxylic acids enhance corrosion resistance of bio-oil. Amounts of water reduce the calorific value of the bio-oil. Aldehydes and other labile compounds make the bio-oil coking or polymerize easily during storage, with the increased viscosity, affecting the quality of the bio-oil. In this experiment, in order to reduce the content of carboxylic acid in bio-oil, the carbon-based solid acid catalysts were used to catalyze esterification of bio-oil. In the experiment, 4 kinds of carbon-based solid acid catalysts were prepared by incomplete carbonization and carbonization-sulfonation. They were starch-TsOH, sucrose-TsOH, glucose-TsOH and corn flour-sulfuric acid. The catalysts were characterized by FTIR (Fourier transform infrared spectroscopy), indicating that the carbon-based solid acid catalyst is an aromatic carbon compound with sulfonic groups. Esterification was carried out with acid and alcohol as model compounds. Among the 4 catalysts, starch-TsOH had the highest esterification rate, and the conversion of acetic acid reached 91.58%. The effects of reaction temperature, reaction time, catalyst mass fraction and ratio of alcohol to acid on the conversion of acetic acid were investigated by single factor experiment. Response surface methodology was used to optimize the catalytic esterification conditions of the bio-oil model compound. The optimum reaction conditions were as follows: reaction temperature 100 ℃, alkyd ratio 3.37, reaction time 2.49 h, and catalyst mass fraction 5.26%, and the acetic acid conversion rate reached 95.51%. Under these conditions, 3 validation experiments were carried out, the conversion rates were 94.89%, 94.26% and 95.01%, respectively, and the relative deviation was 0.83%, which was very close to the predicted value. This indicated that the model was reliable for the analysis and prediction of the optimum esterification conditions. Under the optimum reaction conditions, the starch-TsOH catalyst was reused 5 times, and the activity of the catalyst was investigated. The results showed that the catalyst was deactivated seriously after 4 times, and the conversion rate of acetic acid was reduced to 52.14%. After esterification of bio-oil with methanol, ethanol and n-butanol, the carboxylic acid was converted into neutral ester, and the acid value was reduced by 82.82%-91.41%. Moreover, after esterification, the density and viscosity of bio-oil decreased obviously, and the calorific value increased. The bio-oil and esterified bio-oil were analyzed by FTIR and GC-MS (gas chromatography - mass spectrometer), which showed that some carboxylic acids in bio-oil were converted into esters, some acetals were produced, and phenols were unchanged basically. So, in the future experiments, we should consider how to make better use of phenolic compounds. After esterification and dehydration of bio-oil, the water content of bio-oil was reduced to 2.5%, and the calorific value was increased. The effect was significant, which indicated the necessity of water separation.