The invention provides a steady-state testing device and a steady-state testing method for modularized multi-level converter valves. The device comprises a load electric reactor, a sample valve, an auxiliary valve, a water cooler, a direct-current power supply, a controller and a protection device. Current alternating components and current direct components of the electric reactor can be controlled individually. The structure of a steady-state testing circuit is simple. The steady-state testing device and the steady-state testing method have the advantages that the auxiliary valve and the sample valve are controlled to be unlocked and locked in a charging phase and a testing phase, support capacitors in the auxiliary valve and the sample valve are charged in different phases, and steady-state testing of the modularized multi-level converter valves is realized; charging and energy supplement of the support capacitors in the auxiliary valve are performed only through N output interfacesin the direct-current power supply, and additional direct-current power supplies are not needed for charging of the support capacitors in the sample valve, so that the cost of the whole test circuitis low; the actual working conditions of the modularized multi-level converter valves can be represented completely.