By means of a high-resolution spectroscopic detection system, the radial profiles of plasma poloidal rotation velocity have been measured from the Doppler shifts of impurity ion lines OⅡ464.2nm, CⅢ464.7nm and the hydrogen Hα line on the CT-6B Tokamak. The results show that inside the plasma, the poloidal rotation velocity of impurity ions is in the electron diamagnetic drift direction and reaches its maximum value of～3.5km/s at the minor radius around 9cm. It reverses to the ion diamagnetic drift direction with its maximum value at r=10cm near the limiter. The internal electric field deduced from these data is directed towards the plasma center, and its maximum value is 18V/cm. There is also a poloidal rotation velocity component for neutral hydrogen but it is only in the electron diamagnetic drift direction with a value notably less than that of the ions. A preliminary discussion of the results is also given.