The invention relates to a three-terminal direct current power transmission system and a control method for convertor stations of the three-terminal direct current power transmission system. By virtueof setting of two switch combinations in three convertor stations, quick switching of the operation modes of the convertor stations for switching one convertor station from a rectifying mode into aninversion mode and switching another convertor station from an inversion mode into a rectifying mode can be realized by only controlling on-off of the corresponding switch combinations, thereby ensuring reliable switching of the operation modes, lowering investment and cost, and realizing higher fault response speed.