In this paper, a new type of chemical conversion was prepared on the surface of magnesium alloy in order to improve the corrosion resistance. With the potassium ferricyanide as the main film forming material, A chemical conversion film with good corrosion resistance was prepared on the surface of magnesium alloy by chemical immersion method. The effect of aging time on corrosion resistance of potassium ferricyanide conversion coating on AZ31B magnesium alloy. The scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) were used to analyze and characterize the film surface morphology and the film composition, the electrochemical method and the hydrogen evolution experiment were used to study the corrosion resistance of conversion coating, and the immersion experiment was used to explore the life of the film. The images proved that an about 20 μm layer of film with fewer cracks was formed on the surface of the magnesium alloy substrate. XPS, XRD and EDS results showed that the main component of the film is Fe4[Fe(CN)6]3. The potentiodynamic test results proved that the 12-hour-aged film had the best corrosion resistant compared with the untreated magnesium alloy samples. Its self-corrosion potential was positively shifted by about 1000 mV, and the corrosion current density was reduced by about 3 orders of magnitude. The AC impedance spectroscopy results demonstrated that the charge transfer resistance (Rct), that is 41 380 Ω.cm2, was the largest when the aging time was 12 h, which has remarkably improved compared with the samples at different aging time. The hydrogen evolution experiment results also proved that the potassium ferricyanide conversion coating aged for 12 hours significantly improved the corrosion resistance of the AZ31B magnesium alloys. In summary, potassium ferricyanide chemical conversion film can improve the corrosion resistance of magnesium alloy, the best aging time is 12 h and its service life can be maintained at least 48 hours.