NOVELTY - Processing drainage oil comprises adding filtered drainage oil with catalyst to obtain mixture; sending mixture into a reaction device and separating different products according to difference of boiling point of each component; discharging biochar from gas at high temperature and under high voltage, and removing sulfur, carbon and impurities; sending oil product in a voltage stabilization device and into a high temperature separator to process oil-gas and oil-water separation; and continuously producing biodiesel, gas and water waste solution by a rectifying device.    USE - Method for processing drainage oil (claimed).    ADVANTAGE - The method can effectively recycle drainage oil and produce biodiesel. The reaction kettle is used to perform a one step method of processing double reaction of catalytic cracking and catalytic reforming. Further, the waste solution does not need to be discharged but can be mixed with other biomass waste to generate chemical products of high additional value.    DETAILED DESCRIPTION - Processing drainage oil comprises:    (A) adding filtered drainage oil with catalyst to obtain mixture;    (B) sending mixture into a reaction device through a charging device, and separating different products according to difference of boiling point of each component in conditions of different temperatures and different pressures;    (C) discharging biochar from gas through a carbon removing device in the filter device at high temperature and under high voltage, and removing sulfur, carbon and impurities;    (D) sending oil product in a voltage stabilization device and into a high temperature separator to process oil-gas and oil-water separation;    (E) continuously producing biodiesel, gas and water waste solution by a rectifying device;    (F) completing production of chemical products of high additional value through a reaction device;    (G) automatically controlling the device; and    (H) tempering as a specified biodiesel index according to national standard.