Existence condition and phase transition of Reissner-Nordstrom-de Sitter black hole

After introducing the connection between the black hole horizon and the cosmological horizon, we discuss the thermodynamic properties of Reissner-Nordstrom-de Sitter (RN-dS) space-time. We present the condition under which RN-dS black hole can exist. Employing Ehrenfest' classification, we conclude that the phase transition of RN-dS black hole is the second-order one. The position of the phase transition point is irrelevant to the electric charge of the system. It only depends on the ratio of the black hole horizon and the cosmological horizon.