The measurement technique of constant temperature anemometry was used to study experimentally the mechanism of drag reduction in turbulent boundary layer with riblet surface.Time sequence signals of longitudinal velocity component and normal velocity component across turbulent boundary layer in the wind tunnel over riblet surface and smooth surface have been finely measured by IFA300 constant temperature anemometer with resolution higher than Kolmogorov scale

together with single-hot-wire-sensor probe and double-hot-wire-sensor probe.The ejection and sweep process of coherent structure burst event were identified by wavelet coefficients of longitudinal fluctuating velocity component.Phased-average waveforms of longitudinal and normal fluctuation velocity

as well as Reynolds stress component of coherent structures burst in turbulent boundary layer were extracted by the conditional sampling technique.The statistic characteristics of coherent structure

such as burst period

phased-average waveforms over riblets surface and smooth surface turbulent boundary layer were compared to clarify the effect of drag reduction over V-grooved riblets surface.The mechanism of drag reduction in turbulent boundary layer over V-grooved riblets surface was studied from the view of multi-scale coherent structure passive control.