The pinning mechanism of SDW condensate associated with the imperfect
nesting effect was investigated with the measurement of the temperatur
e dependence of the threshold electric field E(T) for the depinning of
SDW in (TMTSF)2ClO4 for various anion quenching rates. The relatively
strong temperature dependence of E(T) observed in the most rapidly qu
enched phase with T(C)=5.85 K is described by the 3-dimensional impuri
ty weak pinning. With decreasing the quenching rate, the temperature d
ependence of ET becomes gradual for T(C) >3 K. This behavior is explai
ned by the change of pinning mechanism to the strong pinning. For much
lower quenching rate (T(C)<3 K), the temperature dependence of ET bec
omes steeper again and is attributed to the increase of imperfectness
of nesting of Fermi surface. It is understood that the SDW pinning is
provided by the disordered array of anion.