  We have carried out CO J=2-1 and CO J=3-2 observations toward Tycho's
supernova remnant (SNR) using the KOSMA 3m-Telescope. From these observations
we identified three molecular clouds (MCs) around the SNR. The small cloud in
the southwest was discovered for the first time. In the north and east, two MCs
(cloud A and cloud B) adjacent in space display a bow-shaped morphology, and
have broad emission lines, which provide some direct evidences of the SNR-MCs
interaction. The MCs is revealed at -69~-59 km \s, well coincident with the
Tycho's SNR. The MCs associated with Tycho's SNR have a mass of ~2130 sun
masses. Position-velocity diagrams show the two clouds adjacent in velocity
which means possible cloud-cloud collision in this region. The maximum value
(0.66) of integrated CO line intensity ratio I(CO J=3-2/CO J=2-1) for the three
MCs agrees well with the previous measurement of individual Galactic MCs,
implying that the SNR shock just drove into the MCs. The two MCs have a line
intensity ratio gradient. The distribution of the ratio appears to indicate
that the shock propagates from the southwest to the northeast.
