  In this work we use the heavy-quark-light-diquark picture to study the
semileptonic decay $\Lambda_b \to \Lambda_c+l+\bar{\nu}_l$ in the so-called
hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for
larger $q^2$ (corresponding to small recoil), which is the invariant mass
square of $l+\bar\nu$, whereas the perturbative QCD approach for smaller $q^2$
to calculate the form factors. The turning point where we require the form
factors derived in the two approaches to be connected, is chosen near
$\rho_{cut}=1.1$. It is noted that the kinematic parameter $\rho$ which is
usually adopted in the perturbative QCD approach, is in fact exactly the same
as the recoil factor $\omega=v\cdot v'$ used in HQET where $v$, $v'$ are the
four velocities of $\Lambda_b$ and $\Lambda_c$ respectively. We find that the
final result is not much sensitive to the choice, so that it is relatively
reliable. Moreover, we apply a proper numerical program within a small range
around $\rho_{cut}$ to make the connection sufficiently smooth and we
parameterize the form factor by fitting the curve gained in the hybrid scheme.
The expression and involved parameters can be compared with the ones gained by
fitting the experimental data. In this scheme the end-point singularities do
not appear at all. The calculated value is satisfactorily consistent with the
data which is recently measured by the DELPHI collaboration within two standard
deviations.
