Abstract: The long stripe coherent structure of the turbulent boundary layer in a small-scale vertical rectangular channel was observed by using hydrogen bubble flow trace visualization technique. The statistical properties of the long stripe in the experimental channel boundary layer were compared with that in the smooth flat plate boundary layer. The pitch characteristics were explained by the formation mechanism of the long stripe. It was analyzed that how the change of y⁺ affected the distribution of the long stripe. In addition, the frequency characteristics of the long stripe were also investigated, and the correlation of the long stripe frequency in such a flow channel was obtained.