  We present a detailed analysis of the soft X-ray emission of 3C445 using an
archival Chandra HETG spectrum. Highly-ionized H- and He-like Mg, Si and S
lines, as well as a resolved low-ionized Si K$\alpha$ line, are detected in the
high resolution spectrum.
  The He-like triplets of Mg and Si are resolved into individual lines, and the
calculated R ratios indicate a high density for the emitter. The low values of
the G ratios indicate the lines originate from collisionally ionized plasmas.
However, the detection of a resolved narrow Ne X RRC feature in the spectrum
seems to prefer to a photoionized environment. The spectrum is subsequently
modelled with a photoionization model, and the results are compared with that
of a collisional model. Through a detailed analysis on the spectrum, we exclude
a collisional origin for these emission lines. A one-component photoionization
model provides a great fit to the emission features.
  The best-fit parameters are log$\xi$ = $3.3^{+0.4}_{-0.3}$ erg cm s$^{-1}$,
$n_{H}$ = $5^{+15}_{-4.5}\times10^{10}$ cm$^{-3}$ and $N_{H}$ =
$2.5^{+3.8}_{-1.7}\times10^{20}$ cm$^{-2}$.
  According to the calculated high density for the emitter, the measured
velocity widths of the emission lines and the inferred the radial distance (6
$\times$ $10^{14}$ - 8 $\times$ $10^{15}$ cm), we suggest the emission lines
originating from matter locate in the broad line region (BLR).
