The present invention discloses a ballast water level monitoring system. The system comprises a plurality of portable mobile terminals and ballast water level detection units arranged in each ballastcabin in a ship and configured to detect a ballast water level, and the mobile terminals are in wireless network connection with the ballast water level detection units. An embedded water level measurement system is employed to achieve automatic measurement of ship ballast water, automatic alarm can be performed when a water level reaches a set water level, the system is provided with the mobile terminals which are convenient for sailors to carry with, the mobile terminals can prompt the sailors to close a water pump and a valve at any time when the ballast water level reaches a set value, thesystem also can employ the sailors' mobile phones as the mobile terminals to display a current ballast water level and give alarm information when the water level reaches the set value, and therefore, occurrence of an overflow accident of ballast water can be avoided while reducing the manual labor intensity.