Randomized controlled trial(RCT)is the golden standard design to make causal inference on intervention effects in clinical trials.While，in the research reality of Chinese medicine，RCTs could not be conducted，even not applicable，due to ethical issue，characters of the intervention，cost，time and external validity.The essence of causal inference is counterfactual framework.All kinds of covariates could be balanced in RCTs via randomization.Propensity score(PS)is a composite score which could balance the distribution of covariates between intervention and control group.PS could provide unbiased estimate of intervention effect when critical assumptions are met.For the observational studies of Chinese medicine，such as prospective cohort study，PS will have wide application and huge potential.