A bio-demulsifier is applied for crude oil dehydration of fine powder including ferrous sulfide. The present invention is characterized in that the components have the following weight portions: a. 8.5 to 12.0 percent of water solution including 0.05 percent of polypeptide coupling reagent; b. 0.3 to 0.9 percent of magnesium sulfate MgSO4.7H2O; c. 0.4 to 0.8 percent of sodium nitrite; d. 0.1 to 0.3 percent of vitamin C; e. 25 to 30 percent of demulsifier ZS-8901; f. 0.05 to 0.2 percent of INTECHEM-01 fluorocarbon surfactant; g. 20 to 25 percent of methanol; h. the rest of water. The effect is that the bio-demulsifier is conducive to processing the crude oil with fine powder including ferrous sulfide. When the dehydration temperature is 50 DEG C and the adding amount is 80 to 100mg/l, the water content of the dehydrated crude oil is less than 0.5 percent and the oil content of the sewage is less than 100mg/l.