Direct current(DC) transformer plays an important role in maintaining the stable operation of the DC distribution grid.Dual buck based modular multilevel direct current transformer(DB-MMDCT) is proposed in order to address the shoot through and dead time issue in the half bridge-modular multilevel direct current transformer(HB-MMDCT).The topology and operation principles are discussed.The leakage inductor current and the active power transmission property with different outer phase shift angles and inter-submodule phase shift angles per arm under the quasi square wave modulation scheme are illustrated.Furthermore, capacitor voltage balancing algorithm is given by sorting the capacitor voltages and their charge differences.At last, comparative simulation waveforms between the HB-MMDCT and the proposed DB-MMDCT are illustrated in PSIM when the quasi-square wave modulation is adopted.Results validate the priority of the proposed topology and effectiveness and validity of the corresponding control methods.