The invention discloses a modularization-based multi-level converter flexible direct current transmission device and a system thereof. The modularization-based multi-level converter flexible direct current transmission device comprises a transformer and a converter valve upper bridge arm and/or a converter valve lower bridge arm, a three-phase winding of the primary side of the transformer is respectively connected with three phases of a power grid, the three-phase winding of the transformer is respectively connected with a power unit branch of each bridge arm on the converter valve upper bridge arm and/or the converter valve lower bridge arm, and the converter valve upper bridge arm and/or the converter valve lower bridge arm are/is respectively connected with a load. A main circuit topology structure of the device disclosed by the invention comprises no phase reactor, phase reactance is provided by a secondary winding of the transformer at an alternating current side, and the aim of reducing equipment volume, weight, equipment cost and floor area is reached. According to the system disclosed by the invention, system performance can be improved by virtue of collocation of transformer connection groups and electromagnetic coupling of the transformer, direct electric connection between a network side and a valve side in a circuit topology is removed, impact on the network side is reduced when a system valve side has a fault, and the device and the system which are disclosed by the invention have high engineering popularization and application values.