  In this manuscript, an independent method is proposed to estimate opening
angle of dust torus in AGN, through unique properties of Type-1.9 AGN with
double-peaked broad H$\alpha$ (Type-1.9 DPAGN) coming from central accretion
disk. Type-1.9 AGN without broad H$\beta$ can be expected by the commonly
accepted unified model of AGN, considering central BLRs seriously obscured by
dust torus with its upper boundary in the line of sight. For the unique
Type-1.9 DPAGN, accretion disk originations of double-peaked broad H$\alpha$
can be applied to determine the inclination angle of the central accretion
disk, which is well accepted as substitute of the half opening angle of the
central dust torus. Then, among low redshift Type-1.9 DPAGN in SDSS, SDSS
J1607+3319 at redshift 0.063 is collected, and the half opening angle of the
central dust torus is determined to be around 46$\pm$4\degr, after considering
disfavoured BBH system to explain the double-peaked broad H$\alpha$ through
long-term none variabilities and disfavoured local physical conditions to
explain disappearance of broad H$\beta$ through virial BH mass properties. The
results indicate that more detailed studying on dust torus of AGN can be
appropriately done through Type-1.9 DPAGN in the near future.
