The invention relates to a PM 2.5 agglomerating device. The PM 2.5 agglomerating device comprises a smoke channel and an electric dust remover. The smoke channel comprises a vertical segment, an elbow segment and a horizontal segment. The horizontal segment is divided into a first treating cavity and a second treating cavity. The elbow segment is provided with a separator. Coarse dust particles and fine dust particles in the smoke channel are automatically separated through inertia force. The other end of the horizontal segment is provided with a mixing device, and the horizontal segment is connected with a turbulent mixing agglomerating device which is connected with the electric dust remover. The PM 2.5 agglomerating device has the beneficial effects that under the action of coulomb force and adhesive power, the fine dust particles are agglomerated the first time in the first treating cavity, the primary agglomerated fine dust particles and the coarse dust particles with positive charges enter the mixing device to be agglomerated the second time, agglomerated particles are formed and enter the turbulent mixing agglomerating device to be subjected to turbulent mixing, SO3 in the smoke is effectively condensed and adsorbed, and the particle agglomeration effect is further improved.