  The luminosity and spectral energy distribution (SED) of high-$z$ galaxies
are sensitive to the stellar population synthesis (SPS) models. In this paper,
we study the effects of different SPS models on the measurements of high-$z$
galaxies and the budget of ionizing photons during the epoch of reionization,
by employing each of them in the semi-analytical galaxy formation model {\sc
L-Galaxies 2020}. We find that the different SPS models lead to $\lesssim 0.5$
dex differences on the amplitudes of UV luminosity functions, while the two
modes of the same SPS model with and without the inclusion of binary stars
leads to similar UV luminosity functions at $z \ge 6$. Instead, the binary
stars produce $\sim 40\%$ more ionizing photons than the single stars, while
such differences are smaller than those caused by different SPS models, e.g.
the BPASS model produces $\sim 100\%$ more ionizing photons than other models.
