The invention discloses a linked locking mechanism and an antenna downtilt angle control device. The linked locking mechanism comprises: a mounting frame provided with a mounting position, wherein the mounting position is provided with a mounting through hole and a groove; an output assembly comprising an output shaft and an output gear disposed on the output shaft, wherein the output gear can be elastically reset, one end of the output gear is provided with teeth engaging with the groove, and an abutting member passing through the mounting through hole; and a rotary support provided with a bearing surface abutting the abutting member, and an arc-shaped boss disposed on the bearing surface, wherein the arc-shaped boss comprises a guide end, an anti-reverse end, and a fitting component. When an abutting member of one of the output gears abuts and is fitted to a fitting component of an arc-shaped boss, the remaining output gears are locked, and the abutting member of at least one of the outputs gear forms an anti-reverse fit with the anti-reverse end of one of the arc-shaped bosses. The linked locking mechanism and the antenna downtilt angle control device facilitate positioning and achieve accurate control of an antenna downtilt angle.