The invention discloses a mud flat seawater quality monitoring device, and belongs to a water quality monitoring device. The mud flat seawater quality monitoring device comprises a handle, a pressingrod, a water collecting tank, an overflowing pipe and a water quality monitor. The handle is connected with the pressing rod. The pressing rod passes through a center of the top of the water collecting tank and is connected with the water collecting tank. The top of the water collecting tank is provided with a monitoring hole and an overflowing hole. The overflowing pipe is inserted in the overflowing hole and connected with the water collecting tank. A probe of the water quality monitor is inserted into the water collecting tank from the monitoring hole. The mud flat seawater quality monitoring device has the advantages of higher mechanical property, less electric control equipment and less liability of being damaged, easy maintenance, and convenient moving, can be easily inserted into mud flat and pulled out from the mud flat, and is capable of synchronously collecting liquid and solid samples while monitoring water quality, and avoiding problems that service life of the monitoring device is short, maintenance and replacement cost is high because the monitoring device is fixed on the mud flat traditionally.