The invention discloses a photovoltaic grid-connected system based on a three-phase dual-active-bridge DC-DC (direct current to direct current) converter. The photovoltaic grid-connected system is characterized in that the photovoltaic grid-connected system comprises the three-phase DAB (dual-active-bridge) converter connected with a photovoltaic array power supply, the three-phase DAB converter comprises twelve semiconductor switches, four direct-current capacitors, three high-frequency inductors and a three-phase high-frequency transformer T, each semiconductor switches comprises an IGBT (insulated gate bipolar translator) or an MOSFET (metal-oxide-semiconductor field effect transistor), the three-phase high-frequency transformer is of a Y-Y wire connecting mode, working frequency is higher than 50Hz, the three-phase DAB converter is controlled in a traditional phase shifting manner, a conductive angle of each bridge arm is 180 degrees, an upper arm and a lower arm of each same half-bridge alternately conducted, angles of start conduction of various phases sequentially differ 120 degrees, and the size and flow direction of voltage added at two ends of the serially-connected inductor can be controlled by controlling phase angles between square waves. Electric isolation can be achieved by the three-phase DAB (dual-active-bridge) converter in the photovoltaic grid-connected system, and safety operation of the photovoltaic array power supply is ensured.