  We obtain the pion and the kaon parton distribution functions from the
eigenstates of a light front effective Hamiltonian in the constituent
quark-antiquark representation suitable for low-momentum scale applications. By
taking these scales as the only free parameters, the valence quark distribution
functions of the pion, after QCD evolution, are consistent with the data from
the FNAL-E615 experiment. The ratio of the up quark distribution of the kaon to
that of the pion also agrees with the CERN-NA3 experiment. Supplemented by
known parton distribution functions for the nucleons, we further obtain the
cross section consistent with experimental data for the
${\pi^-\rm{nucleus}}\rightarrow{\mu^+\mu^-X}$ Drell-Yan process.
