For bloom casting, typical quality defects such as midway crack usually occur upon improper cooling control during non-steady casting conditions specially for the production specialty steels,. A key measure to eliminate the defects formation has been presented by the adoption of more sophisticated secondary cooling strategies to balance the surface reheating due to casting speed fluctuation. With the consideration of the complex casting conditions and the characteristics of bloom casters, a dynamic control model for the secondary cooling has been developed in the paper to obtain a reasonable temperature profile and solidification progress for the bloom casting process, which is based on a slice residence time method combined with a multi-level control strategy. The feedback system, based on the difference between the calculated surface temperatures and the predetermined or measured surface temperatures, has been integrated into two-dimensional thermal model. The interlocking protection system between level-1 and level-2 is included in the model together with the data diagnosis and processing. Furthermore, the control model also offers technological interface for the introduction of new steel grades in production and the related modification to the secondary cooling parameters. It is shown from online application that the dynamic control system of secondary cooling for bloom casting is robust during operation and adaptable to any change of real casting conditions. Sound quality bloom castings according to acid etched tests have been obtained from the caster accordingly.