The invention discloses a pretreatment method used for processing old household garbage leachate. The pretreatment method comprises following steps: 1, old household garbage leachate is introduced into an ultraviolet-Fenton reactor, the pH value of the old household garbage leachate is adjusted to be lower than 7, a ferrous ion solution is introduced into the ultraviolet-Fenton reactor, and hydrogen peroxide is introduced into the ultraviolet-Fenton reactor; 2, the ultraviolet wave band in the ultraviolet-Fenton reactor is adjusted, oxidation reaction is carried out under ultraviolet lamp irradiation, and the ultraviolet lamp is coated with a reaction system liquid surface, after oxidation, water discharged from the ultraviolet-Fenton reactor is introduced into a flocculation sedimentationbasin, pH value is adjusted to be higher than 7, and an obtained solution is allowed to stand for precipitation; 4, a supernatant obtained in the flocculation sedimentation basin is introduced into amineralized refuse bioreactor, is subjected to primary filtering using a filter layer A, and is introduced into a nitration reaction layer for nitration and denitrification reaction, after processing, obtained discharged water is introduced into a filter layer B and is discharged. The invention also discloses a device using the pretreatment method. The method and the pretreatment method are capable of improving biodegradability of old household garbage leachate.