The invention provides a DC/DC transformer suitable for a high-voltage high-capacity direct-current power grid. The DC/DC transformer comprises a first alternating-current power supply, a second alternating-current power supply, a first alternating-current voltage converting module, a second alternating-current voltage converting module, a high-voltage valve group unit, a low-voltage valve group unit, a first smoothing reactor and a second smoothing reactor. The first alternating-current power supply and the second alternating-current power supply are connected to the high-voltage valve group unit and the low-voltage valve group unit through the first alternating-current voltage converting module and the second alternating-current voltage converting module. The high-voltage valve group unit and the low-voltage valve group unit are connected in series. A high-voltage end of the high-voltage valve group unit and a low-voltage end of the low-voltage valve group unit are connected with the high-voltage direct-current power grid and a grounding electrode circuit through the first smoothing reactor and the second smoothing reactor. According to the DC/DC transformer suitable for the high-voltage high-capacity direct-current power grid, a double-valve-group structure is used, the transformer can be used in a future direct-current power grid, and the requirement for multi-voltage-class multi-end direct-current system direct voltage converting can be met.