Abstract: The traditional water environment capacity is calculated based on 90% of the designed low flow,having the disadvantages such as single hydrological calculation conditions and hard to control according to the water environment capacity results. This paper considers the monthly changes of water environment capacity under the influence of river flow and pollutants entering the river,and proposes a calculation method for dynamic water environment capacity and river pollution control based on changes in hydrological processes and pollution sources.Taking the Jinzhong section of the Xiaohe River Basin in Shanxi province as an example,the monthly water environmental capacity and the remaining amount of the two-water functional zone in the study basin are calculated,and the MIKE11 model is used to calculate the monthly allowable dynamic pollution load into the river. The results show that:（1） In 2019,the COD and NH3-N water environmental capacity thresholds of Water Function Zone A are 138.37～216.54 t and 6.38～14.19 t,respectively,and the water environment capacity is relatively large in July to October;the COD and NH3-N water environmental capacity thresholds of Water Function Zone B are respectively 417.67～821.05 t and 9.32～29.49 t,and its water environment capacity is relatively small from May to August.（2） On the basis of meeting the water quality target of the water function zone,the allowable river inflow load of Water Function Zone A in 2019 is greater than the current river inflow,with more margin of COD and NH3-N in the flood season;the NH3-N should be reduced by 0.003 and 0.086 t,should be reduced by 0.05 and 0.143 t in Water Function Zone B in January and February respectively. The allowable pollution load from April to July is greater than the actual river discharge,which can be appropriately relaxed. The dynamic water environment capacity calculated in this paper can objectively reflect the actual water environment capacity and the remaining amount under changing hydrological conditions,and gives the allowable threshold of pollutants entering the river under the premise of meeting the water quality target of the river,providing an important reference and new ideas for the water environment protection and management of the river basin.