Particle image velocimetry (PIV) technology was used directly to measure the convection pattern in sodium chlorate (NaClO3) crystal growth. The two-dimensional velocity distributions in the solution of NaClO3 have been obtained from experiments, and the velocity fields were compared with concentration fields that have been obtained by a phase-shift interferometer. The structures of both results of the velocity fields and concentration fields agree well. The coupling action of velocity and concentration was analyzed.