A novel biosensor based on electro-co-deposition of myoglobin (Mb), sodium alginate (SA), Fe3O4-graphene (Fe3O4-GR) composite on the carbon ionic liquid electrode (CILE) was fabricated using Nafion as the film forming material to improve the stability of protein immobilized on the electrode surface, and the modified electrode was abbreviated as Nafion/Mb-SA-Fe3O4-GR/CILE. FT-IR and UV-vis absorption spectra suggested that Mb could retain its native structure after being immobilized in the SA-Fe3O4-GR composite film. The electrochemical behavior of the modified electrode was studied by cyclic voltammetry, and a pair of symmetric redox peaks appeared in the cyclic voltammograms, indicating that direct electron transfer of Mb was realized on the modified electrode, which was ascribed to the good electrocatalytic capability of Fe3O4-GR composite, the good biocompatibility of SA and the synergistic effects of SA and Fe3O4-GR composite. The electrochemical parameters of the electron transfer number (n), the charge transfer coefficient (alpha) and the electron transfer rate constant (k (s)) were calculated as 0.982, 0.357 and 0.234 s(-1), respectively. The modified electrode exhibited good electrocatalytic ability to the reduction of trichloroacetic acid (TCA) with wide linear range from 1.4 to 119.4 mmol/L, low detection limit as 0.174 mmol/L (3 sigma), good stability and reproducibility.