Abstract: Complex accidents may occur when drilling to shale formation in directional wells, even well plug-back accident may occur due to pipe sticking. To solve this problem, research on practice technique was conducted to prevent and handle complex accidents. By the safety and economic-oriented principle and through analysis of formation lithologies, optimization was made on drilling fluid property adjustment, complex accident handling and supporting equipment, and different methods were employed to remove the complex accidents occurred when drilled to shale formations. Analysis and research were conducted to the complex accidents occurred in drilling three directional/horizontal wells: Ma 2-1H, Gaomiao 103D and Lei X, the general characters of complex accidents were analyzed, esp. upon different downhole influence factors. The general drilling situation prior to and after drilling into shale formation, handling process of complex accidents and cause analysis were summarized from point to area and their general characters were found out, then suggestions were made to prevent complex accidents when drilling into shale formation in directional/horizontal wells. Also, experiences were collected from directional/horizontal wells where complex accidents had occurred.