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Objective: To investigate what extent lead-time bias is likely to affect endoscopic screening effectiveness for esophageal cancer in the high-risk area in China.Methods: A screening model based on the epidemiological cancer registry data,yielding a population-level incidence and mortality rates,was carried out to simulate study participants in the high-risk area in China,and investigate the effect of lead-time bias on endoscopic screening with control for length bias.Results: Of 100,000 participants,6,150 (6.15％) were diagnosed with esophageal squamous dysplasia during the 20-year follow-up period.The estimated lead time ranged from 1.67 to 5.78 years,with a median rime of 4.62 years[interquartile range (IQR): 4.07-5.11 years]in the high-risk area in China.Lead-time bias exaggerated screening effectiveness severely,causing more than a 10％ overestimation in 5-year cause-specific survival rate and around a 43％ reduction in cause-specific hazard ratio.The magnitude of lead-time bias on endoscopic screening for esophageal cancer varied depending on the screening strategies,in which an inverted U-shaped and U-shaped effects were observed in the 5-year cause-specific survival rate and cause-specific hazard ratio respectively concing a range of ages for primary screening.Conclusions: Lead-time bias,usually causing an overestimation of screening effectiveness,is an elementary and fundamental issue in cancer screening.Quantification and correction of lead-time bias are essential when evaluating the effectiveness of endoscopic screening in the high-risk area in China.