For the cases of data deleted, the storage structure of equivalence class list table of decision table is presented,
and the definitions of the simplified decision table and core attributes based on the simplified decision table are proposed. It is proved that the core attributes acquired from the definition is equivalence to core attributes of original decision table. Then, the theories and algorithms of updating core attribute are researched and described on two aspects of deleting the object appointed and deleting the objects specified information. Finally, the example is given to verify the effectiveness of the algorithms.