The invention provides a direct-current power electronic transformer and a control method and device thereof, and belongs to the technical field of direct-current power electronic transformers. The control method adopts a control strategy of a Boost voltage ring, a Boost current ring and a voltage balancing ring for a Boost module; aiming at a DC/DC conversion module, a control strategy of a DC/DCvoltage loop and a DC/DC current loop is adopted; the ratio of the voltage measurement value of a high-voltage direct-current bus to the sum of the voltage values of Boost buses of all power conversion units in an input state is calculated to obtain an initial control quantity, and the output value of a Boost current loop is subtracted from the obtained initial control quantity to be used as a control signal of the Boost module; the output value of the DC/DC current loop and the voltage gain of the DC/DC conversion module are used as control signals for the DC/DC conversion module. The direct-current power electronic transformer and the control method and device thereof can improve the operation stability of the control system.