  We discuss the reconstruction of neutrino flavor ratios at astrophysical
sources through the future neutrino-telescope measurements. Taking the ranges
of neutrino mixing parameters $\theta_{ij}$ as those given by the current
global fit, we demonstrate by a statistical method that the accuracies in the
measurements of energy-independent ratios $R\equiv\phi (\nu_{\mu})/(\phi
(\nu_{e})+\phi (\nu_{\tau}))$ and $S\equiv\phi (\nu_e)/\phi (\nu_{\tau})$ among
integrated neutrino flux should both be better than 10% in order to distinguish
between the pion source and the muon-damped source at the $3 \sigma$ level. The
10% accuracy needed for measuring $R$ and $S$ requires an improved
understanding on the background atmospheric neutrino flux to a better than 10%
level in the future. We discuss the applicability of our analysis to practical
situations that the diffuse astrophysical neutrino flux arises from different
types of sources and each point source has a neutrino flavor ratio varying with
energies. We also discuss the effect of leptonic CP phase on the flavor-ratio
reconstruction.
