Objective To propose a method to calculate sample size for survival analysis in single-arm trials.Methods Through theoretical formula derivation,we provided sample size estimation method for survival analysis in single-arm trials.Monte-Carlo simulations using STATA software were conducted to obtain the empirical power,so as to verify the accuracy of the estimated sample size.Results Simulation results showed that,when α =0.025 and α =0.01,the power of the sample size calculated by the formula is in accordance with the predetermined power.Conclusions The formula of sample size estimation we proposed could achieve the predetermined power for survival analysis in single-arm trials.Findings of this study provide reliable basis for sample size estimation of early stage antineoplastic drug clinical studies.