Abstract: As an efficient tool for knowledge acctuisition,formal concept analysis has been applied to many fields. Based on the extents (intents) of a formal context,some concepts of complement context were obtained by the operator‘+’， and it was proved that these concepts includes all the meet irreducible elements (join-irreducible elements) of this com- plement context. Then, the approach to find all the meet irreducible elements (join-irreducible elements) was given. Fi- nally, all the concepts of complement context were obtained.

Key words: Formal contcxt,Complcmcnt contcxt,Conccpt latticc,Irrcduciblc clcmcnt