The invention discloses a cyclone separation apparatus of a dust collector. The apparatus comprises an upstream cyclone separation device and a downstream cyclone separation device which are communicated by a gas passage. The upstream cyclone separation device is equipped with a first cyclone tank; the downstream cyclone separation device is totally arranged above the upstream cyclone separation device, and comprises a plurality of downstream cyclone separators which are connected in parallel, each downstream cyclone separator is provided with a second cyclone barrel, positions of air inlets of the downstream cyclone separators which are connected in parallel are not at the same height, so distance that air flow which runs though the first cyclone barrel at a higher speed to enter an air inlet is longer, and the distance that the air flow runs though the first cyclone barrel at a lower speed to enter the air inlet is shorter, thus the air flow distribution at the air inlets of all thedownstream cyclone separators are even to prevent 'cross air blowby' or 'interference' between the second cyclone buckets, and enhance dust separation effect of the second cyclone buckets.