Al-coating is considered to be an ideal protective coating for steels. Multi-arc ion plating Al-coating is of significance for improving steel corrosion resistance, because multi-arc ion plating has advantages, such as non-toxicity, non-pollution, low-energy consumption, and easy operation etc. In this paper, multi-arc ion plated Al-coatings on 45# carbon steel were prepared by setting different bias parameters (0, -50, -100, -200, -300 V). Their surface and cross-section morphologies were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS). The protective properties of the coatings prepared by different bias parameters were studied by electrochemical means, such as open circuit potential (OCP) measurement, electrochemical impedance spectroscopy (EIS), electrochemical polarization (EI) measurement and neutral salt spray test. The results showed that the number of pores and roughness of the Al-coatings decrease first then increase with the increasing bias voltages. Correspondingly, their OCPs, charge transfer resistances and free-corrosion current densities were stable between -0.72~-0.77 V, (1.50~2.98) × 10⁴ Ω·cm², and (1.18~5.49) × 10^-6 A·cm^-2, respectively. It is worthy noted that the corrosion resistance of the Al-coatings was obviously better than that of the bare 45# carbon steel. Being subjected to neutral salt spray test for 336 h, the Al-coatings still exhibit protective performance to certain extent because of cathodic protection mechanism, especially the Al-coating prepared by -200 V had excellent protective properties. In conclusion, the Al-coating, which was prepared by the following process parameters i.e., target current 55 A, Ar gas pressure 1.0 Pa, and bias voltage -200 V, is compact with better adhesive to the substrate thus exhibits the best protective performance.