Research into the exotic nuclei located far from the line of β stability has attracted much attention in recent years.Thanks to the experimental progress and the development of "next-generation" radioactive isotope beam facilities,more and more exotic nuclei have become accessible.Due to the absence of the repulsive electromagnetic force,more neutrons than protons can be added to a stable nucleus and thus the neutron drip-line lies further away from the line of β stability than the proton drip line.