  We study the effect of the cosmological constant on radial oscillations and
gravitational wave echoes (GWEs) of non-rotating strange stars. To depict
strange star configurations we used two forms of equations of state (EoSs),
viz., the MIT Bag model EoS and the linear EoS. By taking a range of positive
and negative values of cosmological constant, the corresponding mass-radius
relationships for these stars have been calculated. For this purpose, first we
solved the Tolman-Oppenheimer-Volkoff (TOV) equations with a non-zero
cosmological constant and then we solved the pressure and radial perturbation
equations arising due to radial oscillations. The eigenfrequencies of the
fundamental $f$-mode and first 22 pressure $p$-modes are calculated for each of
these EoSs. Again considering the remnant of the GW170817 event as a strange
star, the echo frequencies emitted by such stars in presence of the
cosmological constant are computed. From these numerical calculations, we have
inferred relations between cosmological constant and mode frequency, structural
parameters, GWE frequencies of strange stars. Our results show that for strange
stars, the effective range of cosmological constant is $10^{-15}\,
\mbox{cm}^{-2} \le\,\Lambda\, \le 3\times 10^{-13}\, \mbox{cm}^{-2}$.
