The invention provides a treatment method and device of tank-cleaning sump oil. The treatment method comprises the following steps: heating the tank-cleaning sump oil to 60 to 90 DEG C and carrying out adjusting treatment to obtain adjusted sump oil; separating the adjusted sump oil to obtain recycled oil, sewage and oil-containing solid impurities; carrying out extraction and oil removal treatment on the oil-containing solid impurities to obtain extracted oil and oil-containing residues; carrying out resolving, electro-catalytic oxidation and solid-liquid separation on the oil-containing residues to finish the treatment of the tank-cleaning sump oil. The invention further provides the treatment device of the tank-cleaning sump oil. By adopting the treatment method and device provided by the invention, the solid content and moisture content of recycled oil of the treated tank-cleaning sump oil are low; the oil content of the generated residues is low and the residues are easily dried.