A data processing device for a high voltage direct current (HVDC) transmission system is provided. The data processing device includes a plurality of measuring interface systems (MIS) for measuring a voltage or current in an HVDC transmission system; a bus for transmitting data on the plurality of MISs; and an optical distribution module (ODM) transmitting the data transmitted through the bus to the HVDC transmission system, wherein the plurality of MISs increases counter values according to a data transmission completion signal of the ODM, and an MIS corresponding to the counter value among the plurality of MISs transmits data to the ODM through the bus.