Salt tracer is one of the shallow water velocity measurement methods widely used. Pulse Boundary Model method produced lowered measured velocity at short distances from the salt injection position. In this study, an approach was proposed to estimate the flow velocity accurately. The method involves a two-step procedure. Experiments were made under three flow rates of 12, 24, and 48 L/min and three slope gradients of 4°, 8°, and 12° at six measurement positions of 0.05, 0.3, 0.6, 0.9, 1.2, and 1.5 m from the solute injection positions. The peak velocities by the new method were 0.999 times of the centroid velocities, to indicate that either centroid time or peak time can be equally used to measure flow velocity. The new method significantly improved measurement accuracy of flow velocity at short distances, which is indicated by the almost same measured velocities at all locations of short distances as those at longer distances measured. Velocities measured by the new method were significantly higher than those measured by the Pulse Boundary Model method or the centroid velocities by the traditional salt tracer method. Also, the centroid velocity and the peak velocity by the new method well correlated to those by the traditional volumetric method. The velocities measured by the volumetric method were 0.79(centroid velocity) and 0.78(peak velocity) times of thosed estimated by the new improved method. It is reasonable to calculate the shallow flow velocity by the new method to improve accuracy of water flow velocity at short distance. The new improved method provides an accurate and efficient approach in measuring shallow water flow velocity at short distances.