Abstract: The fourth branch of the multi-bore well Z72-P54Z is in a thin oil layer with average thickness of only 1 m in Zhoufu 90-43 block, DaQing Oilfield, which brings difficulty for multi-bore well drilling design and construction. Based on well track design software, the design model is optimized, which can ensure the utmost passing in the thin oil layer target zone, and can ensure the branch is upside the original hole, so it can decrease the risk of entering the branch hole while running string into original hole. Two multi-bore wells were drilled successfully in DaQing Oilfield, and the branch hole was drilled successfully in the thin oil layer with 1.6 m thickness. It forms a special technology which suits branch hole drilling optimization design in Daqing Oilfield, and it is precedent in China at present.