The present invention discloses a simulation device of a modular multiple-level converter, a simulation system and a simulation method, relating to the technical field of simulation, and the problem of the low efficiency of the electromagnetic transient simulation carried out by an existing electromagnetic transient model is solved. The device comprises a grid model and an equivalent modular multilevel converter which is connected to the grid model. The equivalent modular multilevel converter comprises a first controlled voltage source, a second controlled voltage source, a third controlled voltage source, a fourth controlled voltage source, a fifth controlled voltage source and a sixth controlled voltage source which are equivalent to corresponding bridge arms, each of the controlled voltage sources comprises a plurality of sub module equivalent models in cascade connection, each of the sub module equivalent models comprises a one-way conduction device and a variable resistor which is in parallel with the one-way conduction device. Each of the sub module equivalent models is in one-to-one corresponding connection with the corresponding controlled voltage source, and each of the controlled voltage sources is equivalent to an external circuit connected to the corresponding sub module equivalent model. The simulation device of a modular multiple-level converter provided by the invention is used for carrying out time domain simulation on the modular multiple-level converter.