Abstract: The essence of res judicata is to explain where res judicata effect comes from and how it should be treated theoretically.Borrowing the search achievements in civil action,the essence of res judicata of administrative judgment should include the determinative forces of substantive law and procedural law.Determined by res judicata of administrative judgment,the determinative force of substantive law is aimed at the determinative force of the litigated administrative action instead of administrative counterpart.Only the determinative force of procedural law can restrict both administrative subject and administrative counterpart.To realize the purpose of administrative litigation,res judicata of administrative judgment should not only include the determinative force of proceeding,but also include the determinative force of administrative procedure;it should not only be presented in the later litigation procedure,but also should be applied in the following administrative procedure.Administrative subject can not make proposals opposite to the determinate sentence,nor can it carry out administrative actions conflicting with the sentence in which res judicata has been produced.

Key words: administrative judgment, res judicata, essence