The application discloses an on-line detection system for permeability of a mixture and a control method. The on-line detection system comprises a charging barrel and an air pumping pipeline, a material taking device, a material scraping part, a discharging device and a material exhausting pipe. Firstly, the air pumping pipeline is connected with a main exhaust fan of a sintering machine, the airpumping environment of the permeability of the mixture is closer to the air pumping environment of a main air pump fan during the roasting process of the mixture in the actual production, so that it is guaranteed that the air permeability testing environment of the mixture is closer to the actual production environment, and accurate permeability data of the mixture is obtained; and secondly, on-line testing equipment is provided with the material taking device, the material scraping part and the discharging device, compared with the prior art, a role is played in the need for automatic production to replace manual operation. According to the control method, the material taking device is controlled to take material from the mixture discharged by round roller feeder at the head of the sintering machine, the obtained data of the permeability of the mixture is accurate, and the production operation can be effectively guided.