  We investigate the two-pion interferometry in ultrarelativistic heavy ion
collisions in the granular source model of quark-gluon plasma droplets. The
pion transverse momentum spectra and HBT radii of the granular sources agree
well with the experimental data of the $\sqrt{s_{NN}}=200$ GeV Au-Au and
$\sqrt{s_{NN}}=2.76$ TeV Pb-Pb most central collisions. In the granular source
model the larger initial system breakup time may lead to the larger HBT radii
$R_{\rm out}$, $R_{\rm side}$, and $R_{\rm long}$. However, the large droplet
transverse expansion and limited average relative emitting time of particles in
the granular source lead to small ratios of the transverse HBT radii $R_{\rm
out}/R_{\rm side}$.
