Motor shaft is one of the most important parts of motor, which is widely used in industrial field. The straightness of the shaft has a potentially significant effect on motor performance, which is determined by the straightening process in the manufacturing process of the shaft. Considering the grooved characteristics on the micro-motor shaft and using the classical material mechanics principle, the stress and deformation models of the circular shaft with the grooves during the straightening process are established in this paper. By deriving the straighttening stroke-initial deflection model, an accurate and practical relationship between the straightening stroke and the initial deflection was provided. In order to verify the theoretical straightening model, some grooved shaft specimens are designed and manufactured for the straightening experiments. Through the simulation and experimental research, the straightening stroke-initial deflection model for the micro-motor shaft is compared and analyzed, and the correctness and feasibility of the model is verified.