Abstract: Although the original horizontal well trajectory in Halahatang block can meet the demand drilling,its build-up rate is slightly lower,causing long directional time,and extended time of orientation tools in well bottom,which increases the risk of tool failure under high temperature.In order to decrease this hazard,from the view of optimizing build-up rate,the maximum passing curvature of different casing and build-up capacity of tools were calculated.Double-increase trajectory chose a build-up rate of 7 degrees per 30 meters at the first section,and 10 degrees per 30 meters at the second section according to build-up rate on site.Landmark software was used to calculate whether the new trajectory and change in vertical depth affect the choice of PDM,and whether the drilling and casing string can run into the well bottom safely,as well as the change of drag.The calculated results showed that the design with higher build-up rate was reliable. Moreover,field application showed that the optimized profile was favorable for trajectory control and shortened the direction time.