In a randomized controlled trial (RCT), in order to evaluate the possible efficacy and safety of the intervention earlier, you can choose to conduct statistical analysis at a planned time point and manner before the official completion of the trial, which is the interim analysis. In practical research, some observational studies with large investment and long cycle will choose to analyze before the primary analysis node to explore the effects and hypotheses concerned in order to reduce the risk of research. Interim analysis can detect safety problems earlier, reduce research risks, and may obtain statistical conclusions earlier, and discover and adjust defects in the design stage in time, especially the shortcomings of sample size design.