The transition temperature Tt in the growing of poly-Si thin film on amorphous-SiO2, which is prepared by means of electron-beam evaporation (EBE), is evaluated through both simulation and experiment method. Our results demonstrate that there is a sudden transformation in the grain size at transition temperature Tt, and this temperature is apparently influenced by the external factors like the deposition rate F and the substrate material property. Besides, the condition of grain formation at Tt primarily determines the crystallinity of poly-Si thin film, and the relationship between the crystallinity of poly-Si thin film and the transition temperature Tt is also fitted in our work. Thus according to Tt, the parameters of preparation can be predicted and be used to prepare poly-Si to satisfy the needs of the industry through the simple and low-cost EBE method.