The present invention discloses an automatic control method of sintered ore alkalinity. The method comprises the following steps of: when a set alkalinity middle line is known, performing flow time calculation according to a Cao content Ca calculation calculated according to a proportioning model to obtain a predicted sintered ore CaO calculation value; obtaining a correction coefficient J accepting value expressed by a J accepting; obtaining a sintered ore CaO value expressed by a Ca calculation; obtaining a sintered ore SiO value expressed by a sintered ore SiO calculation; calculating a middle line value expressed by a Ca calculation which should be controlled by the sintered ore CaO; calculating a Cao middle line expressed by a Ca calculation middle line which should be obtained through calculation of the proportioning model; dividing a difference between the Ca calculation middle line and the Ca calculation by the predicted sintered ore SiO calculation to obtain a sintered ore alkalinity corrected value; and performing calculation of the proportioning model through changing of the sintered ore alkalinity corrected value, accurately regulating a limestone ratio, and completingalkalinity regulation. The objective of the invention is to provide an automatic control method of the sintered ore alkalinity so that problems can be solved that manual regulation is not in time, personal experiences are heavily depended on and a regulation effect is not stable.