Abstract: In order to find out crude oil production in Guantao Formation and to solve the problem of production capacity decrease due to production in Dongying Formation, CB-A29m well, akey adjustment well, was planned by CNOOC in Chengbei Oilfield. Formations were unconsolidated and hole deviation angle was high, so it was difficult to recover cores from this well. In view of the difficulties in coring operation, the coring system including the core barrel, optimized, and the coring job was successfully finished. Coring practice and knowledge on CB-A29m well have provided new methods for coring design of offshore extended reach appraisal wells during the late development period, and are of great help to coring operation in unconsolidated formations in extended reach high deviated wells.