The invention relates to a DC power transmission system control mode switching method and a DC power transmission system control mode switching system. A system switching device which is in communication connection with DC control protecting equipment and valve control equipment is arranged. In switching, the system switching device performs function switching judgment according to received related information, and furthermore outputs an execution result to the DC control protecting equipment and the valve control equipment. The system switching device is particularly arranged and is only used for switching control modes. Relatively single control mode is realized. Only a switching control strategy exists in the system switching device, and no other control strategy exists, thereby preventing influence of other control strategy, so that the system switching device is particularly used for controlling the control mode. Relatively high control reliability is realized, and furthermore relatively simple switching mode without tedious operations is obtained.