Abstract: To promote the gas field development in Erdos Basin, a set of geo-steering system called Orienteer-LWD was imported from GEOLINK, UK, and the system composition and field applications of this system were described in this paper. Using the geo-steering horizontal drilling technology combined of logging while drilling and mud logging, two horizontal slim holes were drilled successfully. In well SP1, an interval as long as 869.5 m was drilled within the 2.8 m thick gas reservoir using this system, and it totally penetrated 5 sand zones and achieved a four stage horizontal hole. In well DP1, four sidetracking operations were conducted to adjust the well trajectory, which saved the well and drilled a total of 947 m in the ?152.4 mm horizontal interval using this system. The true trajectory of the two wells varies greatly with the designed ones, which refreshed the knowledge to the production zones and explored a new way for developing the complex reservoirs in Erdos Basin.