Image guided surgery (IGS) means that computers are used for modeling the position of patients and providing the surgeons with image guidance for invasive procedures. In this paper, we introduce the composition and the work flow of IGS, analyze the process and principle of Registration, which is regarded as a process to combine the actual position of patients and the visual position of models. Seeing that the precision of the registration determines the precision of the IGS system directly, we conduct a study on the registration algorithm precision, feasibility as well as robustness. Combined with the actual requirements in clinical IGS, we also analyze the influence of changes in the number and position of markers on registration precision.