  We perform a comprehensive investigation of the PSF smoothing effect on the
measurement of concentration-related parameters ($C$, Gini, $M_{20}$) of high
redshift galaxies in the HST and JWST surveys. Our sample contains massive
galaxies from the CANDELS/EGS survey (0 < z < 2), and the CEERS survey (1 < z <
3). The non-parametric concentration-related parameters ($C$, Gini, $M_{20}$)
and the model-dependent parameters (n, Re) of these galaxies are derived from
Statmorph and GALFIT, respectively. We try to evaluate the PSF smoothing effect
by comparing the concentration-related parameters to the S\'{e}rsic index in
both observations and mock images. We find that the concentration index is
generally underestimated, especially for smaller galaxies with higher
S\'{e}rsic index (eventually converging to the concentration index of the PSF).
However, galaxies with lower S\'{e}rsic index ($n \leq 1$) or larger relative
size are less affected by the PSF smoothing effect. The Gini coefficient and
the absolute $M_{20}$ statistic also show similar behaviour as the
concentration index. Caution should be taken for the possible correction of the
concentration-related parameters, where both the relative size and the
S\'{e}rsic index of the galaxy are important. Compared to the HST images, the
PSF smoothing is much less severe for images in the CEERS survey due to the
much higher spatial resolution. In fact, it is better to use the S\'{e}rsic
index rather than the non-parametric morphology indicators to trace the light
concentration for galaxies at high redshifts. From the single S\'{e}rsic
modelling of the HST and JWST images, we also confirm that galaxies at higher
redshift are more compact with smaller $R_e$. The lower mass galaxies are more
disc-like ($n\sim1$) compared to the higher mass galaxies that are more
spheroid dominated ($n\sim3$).
