The invention discloses a fill-in light device for a tunnel detection image capturing device. The fill-in light device comprises a plurality of fill-in lighting units, wherein the fill-in lighting units are applied to the tunnel detection image capturing device; the fill-in lighting units for the tunnel detection image capturing device are uniformly distributed on brackets; the brackets comprise afront bracket, a middle bracket and a rear bracket; the front bracket, the middle bracket and the rear bracket are all parallel to a tunnel tangent surface and are sequentially arranged at a front part, a middle part and a rear part; a first light source group is mounted on the front bracket; a second light source group is mounted on the rear bracket; the image capturing device is mounted on themiddle bracket; the fill-in lighting units are distributed in a 1/4 arch manner on the bracket; the fill-in lighting units can be rotated along the brackets and are locked in locking positions after being rotated; the fill-in lighting units comprise the first light source group, the second light source group and the image capturing device; the first light source group and the second light source group are respectively arranged on two sides of the image capturing device; and lamp covers are mounted on both the first light source group and the second light source group.