The invention relates to a device and a method for controlling concentration of a sand-carrying fluid of a proppant conveying experiment. The device is composed of a fracturing fluid tank 1, a screw pump 2, a dividing three-way joint 16, a closed sand mixing tank 19, a sliding vane pump 7, a sand inlet tank 6, a converging three-way joint 18, a simulating shaft 20, a visualized plate crack 10 anda camera 21. The method comprises the following steps: fixing the visualized plate crack to a support to form a vertical crack; starting the screw pump, wherein the fracturing fluid is divided into anupper flowing part and a forward flowing part at the dividing three-way joint; feeding the upward flowing fracturing fluid into the closed sand mixing tank and mixing the fracturing fluid and a proppant to form the sand-carrying fluid; fully mixing the forward flowing fracturing fluid with the sand-carrying fluid in the sand mixing tank at the converging three-way joint; and injecting the fully mixed sand-carrying fluid into the plate crack through a simulating shaft pump. The device and method are reliable in principle and easy to operate, and improve the accuracy of an experiment greatly, so that a proppant conveying and paying optimized result is of on-site guiding significance.