The invention discloses a flexible direct current transmission submodule, which comprises a first capacitor, an IGBT power unit and a shielding box, wherein an emitter of the IGBT is connected with the shielding box through a driving lead, and a gate of the IGBT is connected with the shielding box through the first capacitor; and the element capacitance of the first capacitor is configured to compensate the balance difference of a Kelvin bridge formed by the interelectrode capacitance of the IGBT and the parasitic capacitance of the shielding box. The invention further discloses a flexible direct current transmission system which comprises the flexible direct current transmission submodule. According to the flexible direct current transmission submodule and the flexible direct current transmission system disclosed by the invention, the interference caused by parasitic capacitance is eliminated by constructing the balanced Kelvin bridge, so that the driving signal tends to be normal, and the working performance of the whole transmission system is ensured.