In medical research, because the number of individuals in the study is usually large, it’s impossible to fully include them in the study. Instead, a sample method is used to randomly select a number of samples from the study population for research, and then the study results are extrapolated to the population. In this paper, we aimed at sampling problems in medical research, systematically describe several commonly used sampling methods and estimation of sample size, and the scope, advantages and disadvantages of various methods. Finally, we conduct case analysis of each sampling method for clinical researchers. Through the introduction of commonly used sampling methods, it provides a reference for clinical researchers to extract research samples in the research.