The invention belongs to the field of the simulation and the control of a power system model, and particularly relates to a clamping double-sub-module type MMC (Modular Multilevel Converter) electromagnetic transient equivalent method. The method comprises the following steps: firstly, according to different trigger signals EN, dividing the operation state of a CDSM (Clamping Double-Sub-Module) into a normal operation state and a locking state; under the normal operation state, jumping into the locking state, and adding a transition state; when EN is equal to 1, judging that the CDSM is under the normal operation state, making the CDSM equivalent to two HBSMs (Half Bridge Sub-Module), and carrying out equivalence exactly according to the equivalent method of HBSM; and when EN is equal to 0, firstly judging whether the previous moment of the EN is the normal operation state or not, jumping into the transition state if the previous moment of the EN is the normal operation state, determining variable resistance according to the judgment logic of the transition state, formally entering the locking state if the previous moment of the EN is not the normal operation state, and judging the variable resistance according to the judgment logic of the locking state. A system node number is lowered, and the simulation speed of CDSM-MMC is effectively improved on the basis of keeping simulation accuracy.