The invention discloses a dealkalization method for red mud. The method comprises a dilute sulphuric acid dealkalization step and a pressure calcium oxide dealkalization step. Red mud is prepared into slurry and introduced into a grinder to be ground; according to the content of alkaline in the red mud, the slurry is slowly added with required dilute sulphuric acid to be ground, filtered and washed to obtain a filter cake and the content of alkaline in the filter cake is analyzed; according to the analyzed content of alkaline in the filter cake, the filter cake is added with calcium oxide and uniformly mixed to be introduced to a high pressure reaction kettle and heated for reaction, and after reaction, the mixture is cooled, filtered and washed; and the obtained filter cake is dried and content of alkaline in the dried filter cake is analyzed. The invention can use only the pressure calcium oxide method to carry out dealkalization of the red mud. Red mud subjected to dealalization treatment of the method has low alkaline content and can be used more in fields such as concrete production, high quality brick and transformed brickproduction. The method solves the problem of the red mud of severe pollution and achieves remarkable economic and social benefits.