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. 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, this paper was made in well trajectory control, bottom hole assembly optimization design, coring tools matching and coring parameters optimization. The application effect was achieved in Shu35-P27 well.