During drilling directional and horizontal wells, the effect of trajectory control quality of the vertical section on the trajectory control of the following directional section is usually neglected. In domestic requirements on the quality of trajectory control, the effect of displacement, inclination and azimuth on the following trajectory control of the directional section is not given necessary attention. For directional and horizontal wells, the deviation in the vertical section not only jeopardizes the trajectory control and completion operations, but also bring negative effect on the well deployment in the oilfield; meanwhile, it may lead to well collision in the vertical section of wells from the same platform. This paper analyzes the deviation results of directional and horizontal wells completed in recent years, and describes the reasons why these deviations were formed. Based on that, this paper further analyzes the effect of the deviation and gives the proposal to deal with it.