This study investigates the relationship between carbonization degree and tetracycline adsorption capacity of biochar, constructing a standardized microscopic model and exploring potential reaction mechanisms. The results show that the adsorption capacity of biochar for tetracycline increases from 16.08 mg L⁻¹ to 98.35 mg L⁻¹ with increasing carbonization degree. The adsorption energy is strongly correlated with aromatic condensation, exhibiting a linear relationship (r² ≥ 0.94). For low carbonization degrees, adsorption is primarily driven by chemical bonds (69.21%), while for high carbonization degrees, it is mainly determined by hydrogen bonding, van der Waals forces, and π-π interactions (91.1%). Larger carbon clusters result in stronger and more stable adsorption interactions. Carboxyl-functionalized highly carbonized biochar displays the highest reaction energy of −1.8370 eV for adsorption through electrostatic interactions. The study suggests that high aromatic condensation in the carbon structure of biochar is crucial for efficient tetracycline adsorption.This study investigates the relationship between carbonization degree and tetracycline adsorption capacity of biochar, constructing a standardized microscopic model and exploring potential reaction mechanisms. The results show that the adsorption capacity of biochar for tetracycline increases from 16.08 mg L⁻¹ to 98.35 mg L⁻¹ with increasing carbonization degree. The adsorption energy is strongly correlated with aromatic condensation, exhibiting a linear relationship (r² ≥ 0.94). For low carbonization degrees, adsorption is primarily driven by chemical bonds (69.21%), while for high carbonization degrees, it is mainly determined by hydrogen bonding, van der Waals forces, and π-π interactions (91.1%). Larger carbon clusters result in stronger and more stable adsorption interactions. Carboxyl-functionalized highly carbonized biochar displays the highest reaction energy of −1.8370 eV for adsorption through electrostatic interactions. The study suggests that high aromatic condensation in the carbon structure of biochar is crucial for efficient tetracycline adsorption.