The invention discloses a salt discharge method in a Bayer-process alumina production; the salt discharge process includes settling tank cooling separation process, cyclone concentration separation, and filter filtration separation. The salt discharge method is characterized in that an underflow cooled and separated by a settling tank is separated by a cyclone classifier; most of separated coarse particles are discharged via an underflow port of a cyclone, then enter a belt type vacuum filter and are filtered; most of separated fine particles are discharged via an overflow port, enter a rotary drum vacuum filter and are filtered. According to the method, the cyclone, the rotary drum vacuum filter and the belt type vacuum filter are in reasonable collocation use; according to the needs of the salt discharge vacuum filter on the carbonate particle size, the cyclone is used for sorting the particle size of the salt discharge settling underflow, the thickness of a filter cake of the rotary drum vacuum filter can be improved, the liquid attached amount of the filter cake of the filter is lowered, the use amount of water for washing cloth and the rotary drum vacuum filter stopping water boiling frequency and water boiling time are effectively reduced, and the productivity of the salt discharge vacuum filter is increased by 40%-50%.