An optical visualization apparatus has been designed to measure the particle velocity of concentrated particle suspensions in a stress controlled rheometer equipped with a quartz parallel-plate. Suspensions with high and low matrix viscosity were used to investigate the nonlinear rheology and the local flow mechanism, as well as the correlations between particle velocity profiles and transition behaviors. Herein, it is shown that the sedimentation has great effects on the flow behavior of suspensions and on the particle velocity profiles. Local flow behaviors e.g. shear banding, drift in the center position of oscillatory shear and dynamic wall slip, have been studied comprehensively. By Fourier-transform rheology (FTR) analysis, the shear banding phenomenon is proved to be strongly linked with the nonlinear rheology of suspensions.