The invention provides a plate shape control method for a steel plate. The phase control method is characterized by comprising the following steps: a tertiary computer system calculates a mu value of to-be-rolled plate blank according to calculating formula: a rectangular conversion coefficient mu= extension ratio/( broadening ratio-1)/2=(target length of the steel plate/length of blank)/[(target width of the steel plate/blank width)-1]2; a secondary computer system selects a rolling strategy according to the mu value, a 3T rolling way of longitudinal rolling, transverse rolling and longitudinal rolling is adopted if mu is smaller than or equal to 20; and a rolling way of longitudinal rolling and transverse rolling is adopted if mu is greater than 20. According to the plate shape control method provided by the invention, specification shape of the steel plate can be effectively improved, rectangular dimension of the steel plate is guaranteed, the defect that the head and the tail are narrow in a steel plate flame cutting process is reduced and a steel plate dimension in-stock rate is reduced, so that the in-stock rate is reduced to 0.03% from 0.16% due to the fact that the head and the tail of the steel plate are narrow, and therefore, a steel plate quality qualified rate is greatly increased, in-stock loss is reduced, and economic benefits of enterprises are increased.