Compared with AC (alternating current) transmission, DC(direct current) transmission has obvious superiority at high power, long distance, submarine cable transmission and asynchronous interconnected between exchange systems etc.. This paper constructed a kind of 12 pulse bridge UHV DC transmission system that includes control protection function through MATLAB/Simulink tool. By setting the breaker parameters, this paper studied the 12 pulse bridge UHV DC transmission system AC/DC side in case of setting down time, type and cleared. The simulation results demonstrate that this system has a good effect in harmonic control and it has no power compensations in realizing HV DC process, and it can completely work as an important reference in constructing HV DC power grid.