  The matrix element of the weak transition {\Lambda}_b\rightarrow{\Lambda}_c
can be expressed in terms of six form factors. {\Lambda}_Q(Q = b;c) can be
regarded as composed of a heavy quark Q(Q = b;c) and a diquark which is made up
of the remaining two light quarks. In this picture, we express these six form
factors in terms of Bethe-Salpeter wave functions to second order in the 1/m_Q
expansion. With the kernel containing both the scalar confinement and the
one-gluon-exchange terms we calculate the form factors and the decay widths of
the semileptonic decay {\Lambda}_b\rightarrow{\Lambda}_clv as well as
nonleptonic decays {\Lambda}_b\rightarrow{\Lambda}_cP(V) numerically. We also
add QCD corrections since they are comparable with 1/m_Q corrections.
