From the spectral point of view, the generation, growth and decay of fluctuations accompanying large-scale structure in an oscillatory turbulent flow are discussed analyzing the experimental data obtained by multiple-probe hot-wires We found that fluctuations with structures are weak at the beginning of flow deceleration phase but grow rapidly, both in low and high frequencies range, with advance of the phase. These high frequency disturbances are generated at the positions where the high-shear layer appears. Fluctuations accompanied by turbulence structures near the wall get weaker and weaker with advance of the phase which could be account for by the reduction of the ensemble-averaged shear.The average height of the structure gets taller and taller during flow deceleration.