The invention discloses a prefabricating forming device with an adjusting function and an adjusting method thereof, and relates to the field of prefabricated buildings. The prefabricating forming device comprises a base, a fixed moving base is fixedly connected to the top end of the base, a moving mechanism is movably connected to the top end of the fixed moving base, and a model control mechanism is fixedly connected to the top end of the moving mechanism; and a prefabrication model is fixedly connected to the end, away from the moving mechanism, of the model control mechanism, a vibration demolding mechanism is fixedly connected to the side wall of the prefabrication model, the base comprises a fixed base, a connecting supporting rod is fixedly connected to the corner of the fixed base, and the fixed moving base comprises a limiting fixing plate. A connecting fixing groove is fixedly connected to the top end of the limiting fixing plate; and meanwhile, when the device is used, the shape of the model can be freely adjusted by arranging a movable model ejection mechanism, models with different requirements can be more conveniently manufactured, the situation that a large amount of time is spent on manufacturing independent models is avoided, and the manufacturing efficiency is improved.