  Extremely relativistic particles play an important role in various radiative
mechanisms of pulsar radio as well as high-energy emission. It is thus very
essential to estimate the Lorentz factor of these particles in the radiation
regions both observationally and theoretically. In this paper, according to the
frequency dependence of component separation and considering some radiation
processes, we obtain the Lorentz factor and its variation in the radiation
region observationally for seven multi-frequency observed pulsars. It is found
that the Lorentz factor decays substantially in the emission region, and the
decay can not be well understood by all known energy loss processes. This
result hints that there are some unknown processes which are responsible to
loosing energy effectively.
