The invention provides a sand conveying and mixed discharging system and a control method. The sand conveying and mixed discharging system comprises a mixed discharging device, the structure of the mixed discharging device is characterized in that a feeding hopper is arranged at the top of a tank body, a main shaft is vertically arranged in the tank body by penetrating the feeding hopper, the mainshaft is connected with a driving device driving the main shaft to rotate, a booster impeller is arranged below the feeding hopper, the booster impeller is fixedly connected with the main shaft and rotates along with the main shaft, a top opening is formed in the middle of the top of the booster impeller, the bottom of the feeding hopper communicates with the top opening, a side wall opening is formed in the side wall of the booster impeller, the top opening communicates with the side wall opening, a bearing seat is arranged at the bottom of the main shaft, and a sealing device is arranged between the main shaft and the end part of the bearing seat. According to the system, through the arrangement of the structure of the booster impeller, the centrifugal force can be utilized to maintainthe pressure in the tank body, so that an additional pressurized feed tank is not arranged, the equipment structure is greatly simplified, the installation space of the equipment is reduced, and the equipment volume is reduced.