The Instability of Wellbore & Its Trajectory (IWIT) is a key academic and technological problem in the course of drilling, which can exert serious and direct influences on the quality, schedule and benefit of a drilling project. As a result, the research on this subject has attracted a broad attention from the circle. This paper, stresses the significance of the innovation, and discusses in detail such problems as the deviation and control of wellbore trajectory, the instability and control of wellbore, as well as the evaluation method for the characteristics of the penetrated formations, on which relevant academic ideas are expatiated. Finally, this paper discusses the development trend of drilling technology and the kernel problems to be resolved.