Surface functional groups are important components of biochar, and their species and content have a great influence on the properties, performance and applications of biochar. Current quantitative analysis methods for surface functional groups in carbon materials is the Boehm titration method with large sample consumption, multiple operation steps and time-consuming procedures. To address these limitations, we developed a quantitative analysis method for mass molar concentration of trace surface functional groups content of biochar by constructing a proton depletion model, writing a Python program, carrying out acid-base titration experiments, and debugging model parameters. This method enables rapid measurement of the surface functional group content and their corresponding acid dissociation constant pK_afor trace amounts of biochar. By adjusting parameters and training the model, the mass range of biochar applicable to this method was analyzed. It was found that the E_MS of the model was less than 0.002 when the sample mass was 50 mg, and the E_MS of the model was less than 0.001 when the iteration number was set to 20 000. This indicates a high level of accuracy of the measurement results. The relative error between the total amount of surface functional groups on biochar determined by this method and the Boehm titration method was within 2%. In addition, this method reduces biochar used by 95%, shortens the measurement time by more than 10 hours, and greatly simplifies the experimental procedures. It meets the technical requirements for micro-trace and rapid quantitative analysis of surface functional groups on biochar.