By comparing and analyzing the conventional project of sidetracking slim-hole horizontal well and considering the rig ability, this paper puts forward an offshore drilling and completion technology of efficient sidetracking slim-hole horizontal well, including the slim-hole horizontal well drilling, sand control methods optimization and oil-water layer packer. By the application of drilling and completion in 4 adjustment wells in QHD32-6F platform, it shows that with this technology, the operation difficulty can be effectively reduced for small size casing sidetracking and the comprehensive cost of drilling and completion can be greatly reduced. The broad application prospect of this technology is presented.