Abstract: The movement law of saline intrusion in the Modaomenwaterway in the wet and dry years is obtained by the method of the figuresof salinity borderline distribution (SBD). The effect of different runoffsin two years on the movement saline intrusion in the Modaomen waterway iscontrasted. The different runoffs in the wet year and the dry year changethe distance and the speed of the saline water movement, and cause thedifferent saline intrusion disaster. The period law of the half-month forthe saline water movement, which is that the saline water moves oscillatingup during the neap tide and down during spring tide, is not affected by thedifferent runoffs in the wet year and the dry year. The magnitude ofupstream runoff only affects the distance and the speed of the saline watermovement in the Modaomen waterway, but does not change the period law of thehalf-month for the saline water movement.