  We have used the sub-millimeter array to image the molecular envelope around
IRC+10420. Our observations reveal a large and clumpy expanding envelope around
the star. The molecular envelope shows a clear asymmetry in $^{12}$CO J=2--1
emission in the South-West direction. The elongation of the envelope is found
even more pronounced in the emission of $^{13}$CO J=2--1 and SO J$_{\rm
K}$=6$_5$--5$_4$. A small positional velocity gradient across velocity channels
is seen in these lines, suggesting the presence of a weak bipolar outflow in
the envelope of IRC+10420. In the higher resolution $^{12}$CO J=2--1 map, we
find that the envelope has two components: (1) an inner shell (shell I) located
between radius of about 1"-2"; (2) an outer shell (shell II) located between 3"
to 6" in radius. These shells represent two previous mass-loss episodes from
IRC+10420. We attempt to derive in self-consistent manner the physical
conditions inside the envelope by modelling the dust properties, and the
heating and cooling of molecular gas. We estimate a mass loss rate of $\sim$9
10$^{-4}$ M$_\odot$ yr$^{-1}$ for shell I and 7 10$^{-4}$ M$_\odot$ yr$^{-1}$
for shell II. The gas temperature is found to be unusually high in IRC+10420 in
comparison with other oxygen-rich envelopes. The elevated gas temperature is
mainly due to higher heating rate, which results from the large luminosity of
the central s tar. We also derive an isotopic ratio $^{12}$C/$^{13}$C = 6.
