The invention discloses a tail gas post-treatment device which comprises a first post-treatment carrier assembly, a second post-treatment carrier assembly and a mixer assembly, wherein the mixer assembly comprises a housing, a mixing tube and a partition fixedly arranged at the periphery of the mixing tube. The partition is used for dividing the housing into a first space which communicates with the first post-treatment carrier assembly and a second space which communicates with the second post-treatment carrier assembly. The mixing tube comprises at least two first openings and at least two second openings which are separately positioned in the two sides of the mixing tube. The mixer assembly further comprises at least two plates with holes, which are positioned in the mixing tube and are arranged in a staggered mode along the axis of the mixing tube. Therefore, crushing of urea particles is strengthened, and heat exchange is also reinforced.