  Based on the consideration that the black hole horizon and the cosmological
horizon of Reissner-Nordstr\"om black hole in de Sitter space are not
independent each other, we conjecture the total entropy of the system should
have an extra term contributed from the entanglement between the two horizons,
except for the sum of the two horizon entropies. Making use of the globally
effective first law and the effective thermodynamic quantities, we derive the
total entropy and find that it will diverge as the two horizons tends to
coincide.
