Abstract: This article reports our recent experimental study of airfoil flow separation control by flexible serrated trailing edge. The experiments were conducted in a straight-type wind tunnel and a hot-wire anemometer was used to measure the velocity profile downstream of the two-dimensional airfoil. Multi-scale coherent structures within the separated shear layers are analyzed both in the time and frequency domains. The results show that the separation bubble thickness decreases by almost 5% of the chord length, the flexible serrated trailing edge vibrates and deforms adaptively and absorbs nearly 20% of the trailing edge shear layer’s energy, perturbation transmits to the leading edge shear layer, and thus the power spectral density decreases significantly in the lower and larger bandwidth to reduce the noise. The coherent structures’ frequency and amplitude also decrease notably, breaking and inhibiting the large vortex package’s transmission obviously in the separation bubble.