The utility model discloses a pre-turnover mechanism suitable for plastic cup stacking packaging, and relates to the technical field of plastic cup production, the pre-turnover mechanism comprises a support plate 1, a support plate 2 and a support plate 4, a slide block 1 is slidingly arranged on the top of the support plate 1, a slide block 2 is slidingly arranged on one side wall of the support plate 2, and a slide block 3 is slidingly arranged on one side wall of the support plate 4. A turn-over mechanism is arranged on the side, away from the first supporting plate, of the first sliding block and comprises a fixing frame, the fixing frame is fixedly connected to the side wall, away from the first supporting plate, of the first sliding block, the longitudinal section, in the length direction of the first supporting plate, of the fixing frame is in an n shape, and an opening is formed back to the first supporting plate; according to the plastic cup turnover device, the turnover mechanism is matched with the clamping mechanism, the plastic cups conveyed from the conveying belt can be horizontally turned over after being clamped, turnover efficiency is improved, turnover operation of a row of plastic cups can be processed at a time, and time and labor cost needed by turnover are reduced.