  The tetramixing of pseudoscalar mesons $\pi$-$\eta$-$\eta'$-$\eta_c$ and
vector mesons $\omega$-$\rho$-$\phi$-$J/\psi$ are studied in the light-cone
constituent quark model, and such mixing of four mesons provides a natural
source for the intrinsic charm $c\bar{c}$ components of light mesons. By mixing
with the light mesons, the charmonium states $J/\psi$ and $\eta_c$ could decay
into light mesons more naturally, without introducing gluons or a virtual
photon as intermediate states. Thus, the introduction of light quark components
into $J/\psi$ is helpful to reproduce the new experimental data of $J/\psi$
decays. The mixing matrices and the $Q^2$ behaviors of the transition form
factors are also calculated and compared with experimental data.
