Abstract: The removal efficiency of dissolved organic nitrogen (DON) in the algae-laden water using KMnO₄ pre-oxidation and enhanced coagulation sedimentation was studied by experiment. The mechanism was analyzed using molecular weight distribution measuring method and two-dimensional electrophoresis method. The results showed that the optimal working condition happened when KMnO₄ dosage was 1.00 mg∕L, the pre-oxidation time were controlled in 30 min, and the PAC dosage was 20 mg∕L, then the DON removal rates reached 36.0%, the turbidity and algae removal rates reached 88.3% and 93.0%. KMnO₄ pre-oxidation enhanced coagulation sedimentation can be used as an emergency treatment option for the removal of DON when the source water algae bloom.