The invention discloses a tail gas recovery system of a kiln. The tail gas recovery system comprises a tail gas collection system, a dust treatment system, a first purification system, a fractionation system and a gas mixing system which are sequentially connected through pipelines; and a gas inlet of the tail gas absorption system is communicated with an exhaust port of the kiln, and a gas outlet of the gas mixing system is communicated with a gas inlet of the kiln. The system can meet the requirement of part of materials for the high oxygen content in the kiln, the problem that in the prior art, the product quality is unqualified due to the fact that the oxygen concentration required by the process cannot be met after tail gas is recycled is solved, good overall sealing performance is achieved, the problem that the oxygen concentration is reduced due to air entering is solved, use is flexible, adjustment can be carried out according to different situations, the cost of recycling and oxygen using is minimized, waste heat of all positions is fully utilized, and the production cost when the system is started is further reduced.