  We have conducted a large-field simultaneous survey of $^{12}$CO, $^{13}$CO,
and C$^{18}$O $J=1-0$ emission toward the Cassiopeia A (Cas A) supernova
remnant (SNR), which covers a sky area of $3.5^{\circ}\times3.1^{\circ}$. The
Cas giant molecular cloud (GMC) mainly consists of three individual clouds with
masses on the order of $10^4-10^5\ M_{\odot}$. The total mass derived from the
$\rm{^{13}CO}$ emission of the GMC is 2.1$\times10^{5}\ M_{\odot}$ and is
9.5$\times10^5\ M_{\odot}$ from the $\rm{^{12}CO}$ emission. Two regions with
broadened (6$-$7 km s$^{-1}$) or asymmetric $^{12}$CO line profiles are found
in the vicinity (within a 10$'\times10'$ region) of the Cas A SNR, indicating
possible interactions between the SNR and the GMC. Using the GAUSSCLUMPS
algorithm, 547 $^{13}$CO clumps are identified in the GMC, 54$\%$ of which are
supercritical (i.e. $\alpha_{\rm{vir}}<2$). The mass spectrum of the molecular
clumps follows a power-law distribution with an exponent of $-2.20$. The
pixel-by-pixel column density of the GMC can be fitted with a log-normal
probability distribution function (N-PDF). The median column density of
molecular hydrogen in the GMC is $1.6\times10^{21}$ cm$^{-2}$ and half the mass
of the GMC is contained in regions with H$_2$ column density lower than
$3\times10^{21}$ cm$^{-2}$, which is well below the threshold of star
formation. The distribution of the YSO candidates in the region shows no
agglomeration.
