The invention relates to an open-close type fan-shaped harrow mechanical weeding device, belonging to the agricultural machinery field; the open-close type fan-shaped harrow mechanical weeding device comprises two fan-shaped harrows, a fixing device and a power device, the power device comprises a hydraulic pressure device and an expansion rod with hinged holes at two ends; the fixing device comprises two expansion rod support sleeves and a fan-shaped harrow supporting rod with hinged holes at two ends; the expansion rod support sleeves are arranged at the inner sides of the hinged holes of the expansion rod, the hydraulic pressure device is arranged on the expansion rod and is arranged between the two expansion rod support sleeves, and the expansion rod with hinged holes at two ends is driven to do reciprocating movement by the hydraulic pressure device; the hinged holes at the lower end of the fan-shaped harrow are articulated to the fan-shaped harrow supporting rod with hinged holes by hinged pins, and the hinged hole at the upper end is articulated to the expansion rod by the hinged pin; the mechanical weeding device can be hung on a tractor, the opening of the fan-shaped harrow can be controlled, so as to achieve the purposes of avoiding crops and removing weeds among plants.