A switching control method for an isolated bidirectional DC-DC converter including: a first circuit breaking unit breaking a line configured to be connected to a DC grid system when malfunction occurs; a first line breaking unit connected to the first circuit breaking unit in parallel and breaking a line depending on an operation of the DC-DC converter; a first capacitor charging with a voltage supplied from the DC grid system; a first switching unit connected to the first capacitor in parallel and having multiple switches (109a to 109d) in a full-bridge form; a transformer provided with a primary side to which an output terminal of the first switching unit is connected; a second switching unit having multiple switches (113a to 113d) in a full-bridge form connected to a secondary side of the transformer; a second capacitor storing an output voltage of the second switching unit and charging a battery connectable to the secondary side; a switching control unit controlling switching of the first switching unit and the second switching unit (109 and 113); a second circuit breaking unit breaking a line connected to the battery when malfunction occurs; and a second line breaking unit connected to the second circuit breaking unit in parallel and breaking a line depending on operation, wherein bidirectional power flow between the DC grid system and the battery is switched, the method comprising: determining whether a voltage of the DC grid system is equal to or greater than a preset input voltage; turning on the first line breaking unit and the second line breaking unit when the voltage of the DC grid system is equal to or greater than the preset input voltage, and charging the first capacitor and the second capacitor with initial voltages (S103 and S105); detecting the initial voltages of the first capacitor and the second capacitor; turning on the first circuit breaking unit and the second circuit breaking unit when the detected initial voltages are equal to or greater than a first preset reference voltage (S109 and S111); turning off the first line breaking unit and the second line breaking unit after the first circuit breaking unit and the second circuit breaking unit are turned on; detecting, in real time, charge voltages with which the first capacitor and the second capacitor are charged; detecting a load power capacity of a load connectable to the battery; and switching the first switching unit and the second switching unit depending on the charge voltages of the first capacitor and the second capacitor and on the load power capacity, wherein the switching is performed using phase shift modulation, single pulse width modulation (SPWM), and double pulse width modulation (DPWM) switching controls together, wherein, in a case where the charge voltage of the second capacitor is less than a second preset reference voltage, when the load power capacity is lower than a preset reference value of rated capacity of the load, the first switching unit and the second switching unit are switched with the DPWM switching control, and when the load power capacity is equal to or greater than the preset reference value, the first switching unit is switched with the SPWM switching control and the second switching unit is switched with the PSM switching control. determining whether a voltage of the DC grid system is equal to or greater than a preset input voltage; turning on the first line breaking unit and the second line breaking unit when the voltage of the DC grid system is equal to or greater than the preset input voltage, and charging the first capacitor and the second capacitor with initial voltages (S103 and S105); detecting the initial voltages of the first capacitor and the second capacitor; turning on the first circuit breaking unit and the second circuit breaking unit when the detected initial voltages are equal to or greater than a first preset reference voltage (S109 and S111); turning off the first line breaking unit and the second line breaking unit after the first circuit breaking unit and the second circuit breaking unit are turned on; detecting, in real time, charge voltages with which the first capacitor and the second capacitor are charged; detecting a load power capacity of a load connectable to the battery; and switching the first switching unit and the second switching unit depending on the charge voltages of the first capacitor and the second capacitor and on the load power capacity, wherein the switching is performed using phase shift modulation, single pulse width modulation (SPWM), and double pulse width modulation (DPWM) switching controls together, wherein, in a case where the charge voltage of the second capacitor is less than a second preset reference voltage, when the load power capacity is lower than a preset reference value of rated capacity of the load, the first switching unit and the second switching unit are switched with the DPWM switching control, and when the load power capacity is equal to or greater than the preset reference value, the first switching unit is switched with the SPWM switching control and the second switching unit is switched with the PSM switching control.