The invention relates to a method of adding a seed solution when evaporating the mother solution during producing aluminum hydroxide or alumina by a Buyer method, which is characterized in that a coming solution from the previous working step passes through a tail evaporator, a plurality of solution self-evaporators, and a salt removing precipitation tank, an underflow in the salt removing precipitation tank goes into an underflow tank and then passes through a salt removing filter press, the filtered solution after the filter press is merged with an overflow from the salt removing precipitation tank, the merged solution is blended with the liquid alkali, the blended solution flows into a circulation mother solution tank, wherein a part of the underflow in the underflow tank is put into the salt removing precipitation tank as a seed solution, the seed solution is put into the new evaporated mother solution, then the process is circulated. The method of adding a seed solution in the evaporated mother solution has the advantages of avoiding the temporary stoppage of the salt removing precipitation tank, reducing the shock and blockage of the solution flow in the evaporator, making the evaporation process of the mother solution flowing smoothly, enabling the liquid carbon full ratio to lower and lower because of the normal operation of salting out and basifying during evaporatingthe mother solution, making sure the aluminum hydroxide or alumina production to step into good circulation, and lowering appropriately the alkali consumption in the system.