  In the manuscript, we check properties of electron densities $n_e$ traced by
flux ratio $R_{sii}$ of [S~{\sc ii}]$\lambda6716$\AA~ to [S~{\sc
ii}]$\lambda6731$\AA~ in narrow emission line regions (NLRs) between Type-1 AGN
and Type-2 AGN in SDSS DR12. Under the framework of Unified Model considering
kpc-scale structures, similar $n_e$ in NLRs should be expected between Type-1
AGN and Type-2 AGN. Based on reliable measurements of [S~{\sc ii}] doublet with
measured parameters at least five times larger than corresponding
uncertainties, there are 6039 Type-1 AGN and 8725 Type-2 AGN (excluding the
Type-2 LINERs and the composite galaxies) collected from SDSS DR12. Then, lower
$R_{sii}$ (higher $n_e$) in NLRs can be well confirmed in Type-1 AGN than in
Type-2 AGN, with confidence level higher than 5$\sigma$, even after considering
necessary effects including effects of electron temperatures traced by [O~{\sc
iii}]$\lambda4364,4959,5007$\AA~ on estimating $n_e$ in NLRs. Two probable
methods are proposed to explain the higher $n_e$ in NLRs in Type-1 AGN. First,
the higher $n_e$ in NLRs of Type-1 AGN could indicate longer time durations of
AGN activities in Type-1 AGN than in Type-2 AGN, if AGN activities triggering
galactic-scale outflows leading to more electrons injecting into NLRs were
accepted to explain the higher $n_e$ in NLRs of Type-2 AGN than HII galaxies.
Second, the lower $n_e$ in NLRs of Type-2 AGN could be explained by stronger
star-forming contributions in Type-2 AGN, considering lower $n_e$ in HII
regions. The results provide interesting challenges to the commonly and widely
accepted Unified Model of AGN.
