Abstract: To understand the distribution of motion scales of vortices in turbulent open channel flow along water depth. A flume experiment system based on high-resolution particle image velocimetry (PIV) was applied to measure fully developed turbulent open channel flow. Meanwhile, the distribution of motion scale of vortices in turbulent open channel flow along water depth, upwelling, sweep down flow and average swirling strength etc. were analyzed using improved power spectrum estimation. The results indicate that the motion scale of vortices in turbulent open channel flow first increases and then decreases along the water depth. The sweep down flow is more prone than upwelling along the water depth. The swirling strength of prograde vortex is larger than that of ret-rograde vortex at respective water depth. The swirling strength of near-wall region is the greatest. Vortices featured by great swirling strength and small scale occur in the near-wall region, then, the vortex scale becomes greater along the water depth, while it decreases under the inhibitory effect of sweep down flow in surface area.