  The observing signals from pulsar are always influenced by the interstellar
medium (ISM) scattering. In the lower frequency observation, the intensity
profiles are broadened and the plane of polarization angle (PPA) curves are
flattened by the scattering effect of the ISM. So before we analyze the
scattered signal, we should take a proper approach to clear scattering effect
from it. Observing data and simulation have shown that the Stokes phase
portraits $I$-$U$, $I$-$Q$ and $Q$-$U$ are also distorted by the ISM
scattering. In this paper, a simulation is held to demonstrate a scattering and
a descattering of the Stokes phase portraits of a single pulse profile of a
pulsar. As a realization of the simulation method, this paper has studied the
descattering of Stokes phase portraits of lower frequency observation of PSR
B1356$-$60, PSR B1831$-$03, PSR B1859+03, PSR B1946+35.
