In formal concept analysis, formal concepts are constructed based on formal contexts so that the knowledge hidden in formal contexts is formulated. In this paper, the notion of operation of formal contexts is proposed firstly, with which the knowledge coming from different formal contexts can be fused and computed. Further, with respect to (w.r.t.) product of two formal contexts and complement of a formal context, the computation of formal concept lattices is studied in detail. It is also emphasized that the computation of the formal concept lattices w.r.t. other operations of formal contexts can be changed into above calculation.