Abstract: Shengli Oilfeld deployed several horizontal wells for shale oil in Luojia area. There are some differences between shale and ordinary sandstone formations, for example, the shale has abundant swelling minerals and developed microcracks. After entering the formation, the drilling fluid will generate comprehensive effect with clay minerals and microcracks, leading to wellbore extremely unstabilized. Therefore, for shale oil horizontal wells, hole stability is very important. Based on the analysis on shale fracture distribution and mineral composition in Shengli Luojia area, evaluation experiments for drilling fluid hole stability have been conducted, which proved the shale hole stability benefit from oil based drilling fluid. This research has confirmed the shale oil horizontal well drilling fluid systems by means of optimization study. Used in BoYe-H1 well successfully, this system is proved to meet the drilling construction need of drilling orizontal wells for Shengli shale oil formation.