Abstract: n this paper,the LDV has been used to measure the turbulent boundary layer sepa-ration,reattachment and redevelopment over a backward-facing step. The developments of mean velocity,turbulent intensity, flatness factor and skewness factor are obtained in the streamwise direction. According to the velocity distribution,the separation line,reattachment position and the starting position of redeveloped turbulent boundary layer are determined.On the basis of analysing the mean and turbulent characteristics in turbulent boundary laycr region in detail,it is found that,in comparison with the results given in turbulent boundary layer over a smooth flat plate,there is no difference between them exeept the greater value of integral con-stant in Log-Law. In addition,there exists wake law in turbulent boundary layer region,and the wake parameter is equal to 0.29.

Key words: turbulent boundary layer, separated flow, backward-facing steps