In order to solve the problem of non-uniform powder concentration in electrical discharge machining (EDM) working fluid, a mathematical model of powder particle movement in stirred tank was established, and the flow field and solid-liquid suspension uniformity were simulated in this paper. The factors of slot shape, depth-diameter ratio, blade angle, blade installation height, and solid particle volume fraction which affected flow field distribution, solid suspension particle uniformity, and power consumption were researched, and the stirred tank structure was optimized. When the ratio of spherical stirred tank depth to diameter is 0.8, the blade design angle is 45°, and the installation height of impeller blade is 120 mm, the suspension uniformity of solid particles is the best and the power consumption is the smallest. Under the conditions of Al powder concentration 4 g/L, pulse width 175 μs, and pulse interval 75 μs, the powder-mixed EDM experiment of SiC/Al functionally gradient material was carried out with this optimized stirring device. The results show that the material removal rate of powder-mixed EDM increased by 24.82% and the surface roughness decreased by 27.28% than that of the conventional EDM.