The simultaneous and sensitive electrochemical detection of dihydroxybenzene isomers (hydroquinone, HQ; catechol, CC; resorcinol, RS) is of great significance because such isomers can be awfully harmful to the environment and human health. In this paper, by preparing poly(L-arginine) modified glassy carbon electrode (P-L-Arg/GCE) with a simple method, a highly sensitive electrochemical sensor for simultaneously detecting HQ, CC and RS was constructed successfully due to the large surface area, good electronic properties and catalytic ability of P-L-Arg/GCE and the electrostatic action between P-L-Arg (positive) and targets (negative). Under the optimized conditions, the results show that the P-L-Arg/GCE has a wide linear range from 0.1 to 110.0 μM for HQ ,CC and RS. The detection limits for HQ, CC and RS are 0.01, 0.03 and 0.1 μM, respectively. Finally, the proposed sensor was successfully applied in real sample analysis.