  In this work, we evaluate the contributions of the hadronic loops to the
amplitudes of $J/\psi\to PV$ where $P$ and $V$ denote light pseudoscalar and
vector mesons respectively. By fitting data of two well measured channels of
$J/\psi\to PV$, we obtain the contribution from the pure OZI process to the
amplitude which is expressed by a phenomenological quantity
$|\mathcal{G}^{PV}_{S}|$, and a parameter $\alpha$ existing in the calculations
of the contribution of hadronic loops. In terms of $\alpha$ and
$|\mathcal{G}^{PV}_{S}|$, we calculate the branching ratios of other channels
and get results which are reasonably consistent with data. Our results show
that the contributions from the hadronic loops are of the same order of
magnitude as that from the OZI processes and the interference between the two
contributions are destructive. The picture can be applied to study other
channels such as PP or VV of decays of $J/\psi$.
