  We describe the dynamical evolution of hot spots velocity, pressure and mass
density in radio loud active galactic nuclei (AGNs), taking proper account of
(1) the conservations of the mass, momentum, and kinetic energy flux of the
unshocked jet, (2) the deceleration process of the jet by shocks, and (3) the
cocoon expansion without assuming the constant aspect ratio of the cocoon. By
the detailed comparison with two dimensional relativistic hydrodynamic
simulations, we show that our model well reproduces the whole evolution of
relativistic jets. Our model can explain also the observational trends of the
velocity, the pressure, the size, and mass density of hot spots in compact
symmetric objects (CSOs) and FR II radio galaxies.
