Abstract: With the maturity of current detecting technology based on high-frequency ground wave radar, current detecting precision has gained increasing attention. This paper aims at discussing the vector current velocity detecting precision of T/Rm-Rb system from the mean square error, and obtaining the optimal operating region of current velocity detecting. Firstly, the vector current velocity is obtained from the radial current velocity measured by T/Rm monostatic radar system and the hyperbolic current velocity measured by T/Rb bistatic radar system. Then the vector current velocity error is calculated from total differential and divided intoⅠtype error andⅡ type error to discuss the mean square error. I type error means the error resulted from the limited Doppler velocity resolution andⅡtype error means the error resulted from the scattering angle observing. Finally, the geometrical dilution of position is drawn and the optimal operating region of current velocity detecting is obtained. That is: the region near the baseline and the bistatic receiver Rbshould be avoided for vector current velocity detection of T/Rm-Rb system.