An improved and self-developed semisolid preparing and rheomoulding device — rotating barrel rheomoulding machine (RBRM) for light alloys in laboratory is introduced in this paper. It mainly consists of a melting furnace, a shearing system with two relative-rotating conical barrels, a central temperature control unit, gas protection system and a die-casting system. Microstructure-processing relationship of A357 aluminum alloy obtained by the RBRM process is investigated by different intensity of turbulence and different shear rate. The experimental results show that the improved RBRM is capable of eliminating coarse dendrites, and producing small and spherical solid particles uniformly distributed in a eutectic matrix. In addition, the process can eliminate entrapped gas and reduce fine shrinkage pores in the specimens as well. Compared with the original self-developed device in our laboratory, the improved equipment has the following advantages: accurate control of stirring temperature; small volume and convenient manipulation; fine and spherical solid particles, chemical and microstructural uniformity throughout the specimens and so on.