  We study heat conduction in one dimensional (1D) anharmonic lattices
analytically and numerically by using an effective phonon theory. It is found
that every effective phonon mode oscillates quasi-periodically. By weighting
the power spectrum of the total heat flux in the Debye formula, we obtain a
unified formalism that can explain anomalous heat conduction in momentum
conserved lattices without on-site potential and normal heat conduction in
lattices with on-site potential. Our results agree very well with numerical
ones for existing models such as the Fermi-Pasta-Ulam model, the
Frenkel-Kontorova model and the $\phi^4$ model etc.
