  By comparing the properties of non-recycled radio-loud $\gamma-$ray pulsars
and radio-quiet $\gamma-$ray pulsars, we have searched for the differences
between these two populations. We found that the $\gamma-$ray spectral
curvature of radio-quiet pulsars can be larger than that of radio-loud pulsars.
Based on the full sample of non-recycled $\gamma-$ray pulsars, their
distributions of the magnetic field strength at the light cylinder are also
found to be different. We notice that this might be resulted from the
observational bias. In re-examining the previously reported difference of
$\gamma-$ray-to-X-ray flux ratios, we found the significance can be hampered by
their statistical uncertainties. In the context of outer gap model, we discuss
the expected properties of these two populations and compare with the possible
differences identified in our analysis.
