Abstract: Horizontal wells in Biyang sag are generally deployed in spare blocks,with characteristics of thin target layer thickness,serious formation phase change and some differences between real drilling results and the design,therefore,the horizontal wells geo-steering should be specially strengthened.According to horizontal wells practical experience of Biyang sag in the last two years,the basic work before drilling and the conventional technology should be prepared,such as data collection and digestion,determination of controlled layers,analysis of target rationality,and drawing of predicting trajectory profile.Besides that,how to establish accurate geological profile and fine stratigraphic correlation,and how to make a good geo-steering in drilling stage,for example in horizontal section have also been discussed.