In order to study the theoretical basis of Mn(Ⅱ) removal in water by alkali modified pomelo peel biochar, the dynamic adsorption of Mn(Ⅱ) in a fixed bed was investigated. Using flow rate, bed height, and initial concentration of Mn(Ⅱ) as variables, the effects of these three operating conditions on the adsorption of Mn(Ⅱ) in a fixed bed of alkali-modified pomelo peel biochar were studied, and the data were fitted by varying models. The results show that the alkali-modified pomelo peel biochar has a certain buffering effect on the adsorption of Mn(Ⅱ). The fixed bed operation time is prolonged with the decrease of flow rate and Mn(Ⅱ) initial concentration, as well as the increase of bed height. The highest adsorption capacity of alkali modified pomelo peel biochar for Mn(Ⅱ) is observed(25.59 mg/g) when the flow rate is 1 mL/min, Mn(Ⅱ) initial concentration is 150 mg/L and bed height is 2 cm. The Thomas model indicates that internal and external diffusion are not control procedures in the process of adsorption; the Adams-Bohart model suggests that the adsorption preliminary kinetics in the fixed bed is controlled by external mass transfer, and its linear expression (the BDST model) relatively accurately predicts the operation time of effluent Mn(Ⅱ) concentration reaching 70% of influent Mn(Ⅱ) concentration under each initial condition; the modified dose-response model accurately describes the shape of the Mn(Ⅱ) breakthrough curve.