The utility model provides a sliding plate sealing assembly which is novel in structural design and suitable for a large-caliber pipeline. The gate valve comprises a valve body and gates, wherein a round hole is formed in the valve body, an annular flashboard guide groove is formed in the inner wall of the round hole, a through hole which penetrates through the end of the valve body and is communicated with the guide groove is formed in one end of the valve body, the guide groove is rectangular, and the flashboard penetrates through the through hole and is located in the guide groove and can slide in the guide groove; the top side wall or/and the bottom side wall in the guide groove is/are provided with a U-shaped flexible rubber sealing strip arranged in the direction of the guide groove.A flashboard sealing seat is fixedly installed at the front end of the flashboard, an opening communicated with the through hole is formed in the flashboard sealing seat, the flashboard penetrates through the opening, an annular rubber sealing ring is arranged on the inner wall located in the opening, the flashboard penetrates through the rubber sealing ring, and the rubber sealing ring makes contact with the peripheral side wall of the flashboard.