With dimethyldiallylammonium chloride (DM) as the main component to provide the cationic groups, and with hydroxyethyl methacrylate (HEMA) and N,N-methylenebisacrylamide (MBA) as the auxiliary structural monomers, polyelectrolyte hydrogel film P(DM-co-HEMA) can be successfully prepared. DM provids the hydrogel with good anti-swelling properties, hydrolysis stability and conductivity in an aquatic environment. A dopamine (DA) electrochemical sensor (P(DM-co-HEMA)/GCE) can be constructed by using the hydrogel film modified glassy carbon electrode (GCE). The performance test results show that the prepared P(DM-co-HEMA)/GCE exhibits a good electrochemical response to DA. Within the concentration range of 0.1~0.4 mmol/L and 0.4~2.9 mmol/L of DA, the corresponding values of oxidation peak current and reduction peak current increase linearly with the concentration of DA, with a detection limit of 7.41 μmol/L (signal-to-noise ratio of 3), which indicates that compared with bare GCE, P(DM-co-HEMA)/GCE is characterized with a better stability and anti-interference property.