The electrochemical methods with the advantages of sensitivity, accuracy, low-cost, simplicity and real-time online determination are expected to detect organic dyes, Methyl Orange (MO) and Rhodamine B (RhB), which are harmful to human beings extensively. In this work, Fe3O4 and single-walled carbon nanotubes (SWNTs) hybrid, as a non-noble metal electrocatalyst, was synthesized by hydrothermal method and modified on the electrode to prepare an electro-sensor for monitoring MO and RhB. Due to the synergistic effects between Fe3O4 and SWNTs, the magnified surface area and good dispersion of SWNTs, the Fe3O4/SWNTs hybrid, has the outstanding superiority of higher-conductivity and catalytical activity with a wide linear concentration range of 0.025-4000 mu M, 0.1-250 mu M and a calculated low detection limit (LOD) of 4 nM, 25 nM for MO and RhB respectively. Furthermore, it's the first time that the proposed electrode achieves the simultaneous determination of both dyes. Then, from the investigation of kinetics and pH value, it's found that both oxidation reactions involve two electrons and one proton participating. The modified electrode also exhibited good selectivity, high reproducibility and promising feasibility in practical sample analysis.