We apply a simple model to describe the cluster-shell competition in 20Ne due to the spinorbit interaction, which is called Antisymmetrized Quasi Cluster approach. By introducing one additional parameter in the trial wave function, the transformation of one α cluster into a quasi cluster, i.e. the transition from a cluster state [16O+α] to a shell model state [16O+4N], can be studied in details. Such approach can be applied to the case of 3α + four neutrons in 16C, and cluster-shell competition is investigated in a neutron-rich nucleus.