It is difficult to obtain low-dose three-dimensional images of a long sample with high spatial resolution in a single scan using conventional X-ray micro-CT technique because the synchrotron X-ray beam is prolate. Spiral scanning is induced into synchrotron X-ray micro-CT (SR -CT) to resolve this problem. We investigate the effects of some factors on imaging quality and scanning speed by simulation and experiment, such as pitch, vertical beam width and projections per 180. When the pitch is not greater than 2, it is found that the relative error and the CT scanning speed decrease while the projections per 180 increases. The scanning speed increases with vertical beam width. Furthermore, as pitch becomes greater, the scanning speed becomes faster. The relative error is minimized by choosing the appropriate parameters to make the ratio between rotation and vertical transfer be an integer. The simulated results are confirmed by the synchrotron-based spiral micro-CT (SRS -CT) experiments performed at the Shanghai Synchrotron Radiation Facility and parameters are optimized. The results presented herein provide a theoretical and experimental basis for future applications of SRS -CT.