This paper investigates the conditional entropy, \(h _{\mu }(T\mid \langle G \rangle )\) , which is induced by the T-invariant finite partition \(\langle G \rangle \) . Several fundamental propositions are obtained and a corresponding variational principle is proven as follows \(\begin{aligned} \sup _{\mu \in \mathcal {M}(X,T)}h_{\mu }(T\mid \langle G\rangle )= h_{top}(T\mid \langle G \rangle ), \end{aligned}\) where \(\mathcal {M}(X,T)\) is the collection of all invariant measures of X, which is an extension of the usual variational principle. Moreover, this study also consists of its presentation of the commutativity proposition for those conjugate invariants.