The steady state model（classical model）， which is used widely to measure the operation and control performance of the dc transmission， adopts the passive filtering method in the AC side. It cannot overcome the harmonic and reaction’s adverse effects to converter transformer， and the secondary winding of the converter transformer uses Y-Δ wiring， which affects the commutation reactance because of the construction’s asymmetry. This paper analyzes the disadvantages that the classic model has， puts forward a new dc transmission steady state model with a new type converter transformer， compares the construction’s difference with the classical model， expounds the new type converter transformer’s design feature and the new type filtering way that uses the coupling winding’s harmonic ampere-winding balance as the filtering mechanism， and gives the converter’s steady state equation. Through the detailed simulation， this paper compares the simulation results using the classical and new type model and verifies the model’s correctness and the superiority in the harmonic suppression and improving the system steady state operation performance.