Sealed coring can improve the reliability of core analysis data. Water displacing oil efficiency can be inspected; quantitative analysis can be made on the oil-water reservoir dynamics and remaining oil distribution of oil layer through horizontal well sealed coring. This has great significance for making effective production and efficiency increasing measures, increasing individual well producing rate of extremely low abundance layer and reserve producing level, improving the exploitation plan and so on. Sealed coring is more difficult in horizontal well than in vertical well. Based on the analysis on the technical difficulties of sealed coring in horizontal well, the study was made in well trajectory control, bottom hole assembly optimization design, coring tools matching and coring parameters optimization. Good application effect was achieved in Shu35-P27 well.