  In the fusion process, the investigation of the reaction dynamics in the time
evolution of the nuclear configuration is necessary. The neck parameter
$\epsilon$ which is one of the parameters representing the nuclear
configuration in the two center shell model is important in fusion owing to the
nucleons transferring through the neck. The time evolution of the neck has not
been discussed in detail, but is crucial for fusion cross section in the
assessment of new elements synthesis. The dynamical analysis for the fusion
hindrance under the neck formation on the nuclear deformation space has been
done. The fusion probability $P_\text{CN}$ considering the different denecking
motion and the fusion hindrance are discussed. The calculations were performed
using the dynamical model of nucleus-nucleus collisions based on the
multidimensional Langevin equations.The formation of the neck bridge at the
approaching stage is found to be crucial to the fusion hindrance. It is
clarified that the inner barrier appears owing to the change in the degree of
mass asymmetry $\alpha$ with the relaxation of $\epsilon$.The fusion hindrance
occurs because the inner barrier is formed by the early neck formation. The
role of the neck parameter $\epsilon$ is critically important for the fusion
dynamics.
