A fume exhaust device, comprising: a cooking fume separation device comprising: a first bracket, a second bracket, a plurality of first separation plates and a plurality of second separation plates, the plurality of first separation plates being fixedly connected to the first bracket, the plurality of second separation plates being fixedly connected to the second bracket, the plurality of first separation plates and the plurality of second separation plates being staggered and spaced apart in an up-down direction, the first separation plate and the second separation plate partially covering each other to form a plurality of separation passages, and the first bracket and the second bracket being movably connected so as to adjust a size of each separation passage, characterised in that: the first bracket comprises a first horizontal bar and two first vertical bars perpendicular to the first horizontal bar and located at two ends of the first horizontal bar, and the plurality of first separation plates are secured to the first horizontal bar, the second bracket comprises a second horizontal bar and two second vertical bars perpendicular to the second horizontal bar and located at two ends of the second horizontal bar, and the plurality of second separation plates are secured to the second horizontal bar, the second vertical bar defines a groove in a vertical direction, an end of the first horizontal bar and the first vertical bar are slidably embedded in the groove, and an inner side surface of the second vertical bar is fixed with a rack, and a driving device drives the rack through a gear assembly to bring the second bracket to move relative to the first bracket, wherein the fume exhaust device further comprises a fan and a controller, and the controller is configured to control the driving device to adjust a relative position of the first bracket and the second bracket according to a rotating speed of the fan, such that the separation passage becomes larger when a speed level of the fan is increased and the separation passage becomes smaller when the speed level of the fan is decreased. a cooking fume separation device comprising: a first bracket, a second bracket, a plurality of first separation plates and a plurality of second separation plates, the plurality of first separation plates being fixedly connected to the first bracket, the plurality of second separation plates being fixedly connected to the second bracket, the plurality of first separation plates and the plurality of second separation plates being staggered and spaced apart in an up-down direction, the first separation plate and the second separation plate partially covering each other to form a plurality of separation passages, and the first bracket and the second bracket being movably connected so as to adjust a size of each separation passage, characterised in that: the first bracket comprises a first horizontal bar and two first vertical bars perpendicular to the first horizontal bar and located at two ends of the first horizontal bar, and the plurality of first separation plates are secured to the first horizontal bar, the second bracket comprises a second horizontal bar and two second vertical bars perpendicular to the second horizontal bar and located at two ends of the second horizontal bar, and the plurality of second separation plates are secured to the second horizontal bar, the second vertical bar defines a groove in a vertical direction, an end of the first horizontal bar and the first vertical bar are slidably embedded in the groove, and an inner side surface of the second vertical bar is fixed with a rack, and a driving device drives the rack through a gear assembly to bring the second bracket to move relative to the first bracket, wherein the fume exhaust device further comprises a fan and a controller, and the controller is configured to control the driving device to adjust a relative position of the first bracket and the second bracket according to a rotating speed of the fan, such that the separation passage becomes larger when a speed level of the fan is increased and the separation passage becomes smaller when the speed level of the fan is decreased. the first bracket comprises a first horizontal bar and two first vertical bars perpendicular to the first horizontal bar and located at two ends of the first horizontal bar, and the plurality of first separation plates are secured to the first horizontal bar, the second bracket comprises a second horizontal bar and two second vertical bars perpendicular to the second horizontal bar and located at two ends of the second horizontal bar, and the plurality of second separation plates are secured to the second horizontal bar, the second vertical bar defines a groove in a vertical direction, an end of the first horizontal bar and the first vertical bar are slidably embedded in the groove, and an inner side surface of the second vertical bar is fixed with a rack, and a driving device drives the rack through a gear assembly to bring the second bracket to move relative to the first bracket, wherein the fume exhaust device further comprises a fan and a controller, and the controller is configured to control the driving device to adjust a relative position of the first bracket and the second bracket according to a rotating speed of the fan, such that the separation passage becomes larger when a speed level of the fan is increased and the separation passage becomes smaller when the speed level of the fan is decreased.