  The radiation mechanism of Radio-Loud Narrow-Line Seyfert 1 (RL-NLS1) from
X-ray to $\gamma$-ray bands remains an open question. While the leptonic model
has been employed to explain the spectral energy distribution (SED), the
hadronic process may potentially account for the high energy radiation of some
$\gamma$-ray loud Narrow-Line Seyfert 1 (NLS1) as well. We study one of such
RL-NLS1, PKS 1502+036, comparing the theoretical SEDs predicted by the leptonic
model and the lepto-hadronic model to the observed one. For the hadronic
processes, we take into account the proton synchrotron radiation and
proton-photon interactions (including the Bethe-Heitler process and the
photopion process) including the emission of pairs generated in the
electromagnetic cascade initiated by these processes. Our results show that the
leptonic model can reproduce the SED of this source, in which the X-ray to
$\gamma$-ray radiation can be interpreted as the inverse Compton (IC)
scattering. On the other hand, the proton synchrotron radiation can also
explain the high energy component of SED although extreme parameters are
needed. We also demonstrate that the $p\gamma$ interactions as well as the
cascade process cannot explain SED. Our results imply that a leptonic origin is
favored for the multi-wavelength emission of PKS 1502+036.
