The ultra-intense hitting power of abrasive water jet is mainly provided by high-speed abrasives. So measuring the abrasive velocity is the base to research the hitting power and the erosion mechanism. To overcome the shortcomings of traditional research methods, a new testing method was proposed. The method uses the PIV(particle image velocimetry)combined with center recognition program to gain the abrasive velocity, and can test the high velocity of abrasive jet without contacting. Furthermore, the influence law of nozzle structure on the abrasive velocity was proceeded with this method. The results show that increasing the length of straight segment in a certain range is conducive to improve the abrasive velocity, because the abrasives were in the state of obvious accelerated motion in the end of the straight segment. Increasing the length of convergence section in a certain range is conducive to improve the abrasive velocity, but the increase amplitude is not very large. When the convergence angle is too large, liquid phase accelerates slowly in the first half of convergence section but accelerates sharply in the second half of convergence section. Then the acceleration of abrasives lags behind that of liquid phase, and thus the abrasive velocity is decreased.