  By adopting two models of strange and antistrange quark distributions inside
nucleon, the light-cone meson-baryon fluctuation model and the effective chiral
quark model, we calculate the $D_s^+ - D_s^-$ asymmetry in photoproduction in
the framework of heavy-quark recombination mechanism. We find that the effect
of asymmetry of strange sea to the $D_s$ asymmetry is considerable and
depending on the different models. Therefore, we expect that with the further
study in electroproduction, e.g. at HERA and CEBAF, the experimental
measurements on the $D_s^+ - D_s^-$ asymmetry may impose a strong restriction
on the strange-antistrange distribution asymmetry models.
