Abstract: The drilling technology is very important for the fractured granite basement reservoir to reduce the damage of formation and improve the production because of the large difference of lithology, physical property and other formation characteristics between granite and conventional reservoir. After the field application of the fractured granite basement reservoir in KHA Field of Yemen, the unbalanced drilling can prevent the formation damage caused by the solid phase invasion, improve the penetration rate, reduce the loss of drilling fluid and protect the hydrocarbon reservoir. It can reduce the risk of lost circulation, and save the drilling cost. The development of horizontal well can improve fracture drilling ratio, injection capacity of injection well and output of single production well. In addition, it helps to discover new effective reservoir, increase the reserve of oil field and provide important parameters for oilfield development, deployment, infilling and adjustment of wells, thus significantly improve the development effect of fractured granite basement reservoir.