The contradiction between AC/DC interconnected power grid and independent calculation mode adopted by regional control centers， brings in various drawbacks to the analysis and monitoring of a power network. Based on the distributed dynamic power flow for an AC/DC interconnected power grid with asynchronous iteration mode， asynchronous iteration for an AC/DC interconnected power grid considering converter transformer's tap changer regulating is proposed. The AC bus voltage magnitude， phase angle and converter transformer turns ratio are taken as state variables of DC boundary nodes， the proposed algorithm is realized by increasing a fix-point iteration about converter transformer turns ratio. The numerical simulation for an AC/DC interconnected system extended by IEEE standard system show that the converter transformer turns ratio of each subsystem obtained by the proposed algorithm is the same as that of the whole network dynamic power flow calculation， and then the dynamic power flow solution consistent with the whole network can be obtained subsequently.