The invention relates to a distributor and a top cap thereof. The distributor comprises an outer tube, a conveying unit and a blowing unit, wherein the conveying unit is mutually communicated with theouter tube; the blowing unit is positioned in the outer tube; the blowing unit is close to the bottom part of the outer tube; the upper end of the outer tube is also provided with the top cap; the top cap comprises a seal cover and an inner tube; the seal cover is arranged at the upper end of the inner tube and is coaxial to the inner tube; the lower end of the inner tube is positioned in the outer tube; the seal cover comprises a first part and a second part; the first part is coaxial to the second part. The top part of the distributor adopts a way of mutual nesting between the top cap and the outer tube, so that nitrogen which is used for conveying the catalyst can be overflown from a gap reserved between the top cap and the outer tube in time, so that the content of the nitrogen in thedistributor is effectively reduced, the concentration of the nitrogen in a reaction area is reduced, and the reaction area shows a stable micro-boiling state.