  Ultra-fast outflows (UFOs) with mildly relativistic velocities are measured
using the X-ray spectra of radio-quiet and -loud active galactic nuclei (AGNs).
In general, UFOs are believed to be generated from the accretion disk around a
black hole (BH). A line-force driving model is suggested to be the mechanism to
drive UFOs from the accretion disk. In this paper, we use the non-hydrodynamic
approach to examine the influences of radiation-drag effects on the
line-force-driven winds generated from the accretion disk. We find that the
radiation-drag effects can significantly weaken the line-force-driven winds.
Compared with the case without the radiation-drag effects, when the
radiation-drag effects are considered, the maximum speed of winds is reduced by
$\sim$60\%--70\%, the mass outflow rate is reduced by $\sim$50\%--80\%, and the
kinetic power is reduced by about an order of magnitude. The radiation-drag
effects narrow the area where the winds are generated.
