Abstract: The forming and developing process of the separated vortex induced by a spoiler attached to a flate plate is presented. The spoiler is either stationary or oscillatory. When the spoiler is in the stationary state, a separated flow with larger-scale random vortices is formed behind the spoiler. As soon as the spoiler oscillates, induced vortices with definite frequencies appear downstream. The test results show that the scale, intensity, pairing and merging of the vortices depend, to a large extent, on the forced oscillation frequencies of the spoiler. The effects of the oscillation amplitude of the spoiler over the vortex is also discussed.