A process of removing SO2 from a flue gas with a trickling filter using modified ceramsite packing is described. The biological flue gas desulfurization process includes: feeding the flue gas containing sulfur dioxide through the column bottom into the biomembrane trickling filter at certain temperature, contacting with the modified ceramsite biomembrane packing and purifying, which purified flue gas is discharged via the column top; and spraying the nutrient fluid rich in high concentration of the desulfurization strain through the top to the modified ceramsite biomembrane packing, thereby the sulfur-bearing pollution source in the flue gas is degraded, so as to discharge a purified flue gas satisfying the environmental requirements.