Device for the mixing and distribution of fluids for a catalytic reactor with a downward flow, said device comprising a collection zone (A), a mixing zone (B) and a distribution zone (C) comprising a distribution plate (12) comprising at least one first zone (C1) supporting a plurality of chimneys (13) and a second zone (C2); said mixing zone (B) is comprised in an annular enclosure (15) situated in the distribution zone (C), said mixing (B) and distribution (C) zones being delimited by at least one annular wall (16) comprising at least one lateral passage section (17a, 17b) suitable for the passage of the fluids from said mixing zone (B) to the first zone (C1) of said distribution zone (C), and the second zone (C2) comprises a plurality of openings (18) suitable for the partial passage of the fluids out of the distribution zone (C).