Abstract　 　　  

  Long duration gamma-ray bursts (GRBs) are thought to be produced by the core-collapse of a rapidly-rotating massive star. This event generates a highly relativistic jet and prompt gamma-ray and X-ray emission arises from internal shocks in the jet or magnetised outflows. The favored progenitor model for short duration gamma-ray bursts (SGRBs) is the coalescence of two compact stars. One possible is that a rapidly spinning, strongly magnetized neutron star (known as millisecond magnetar) is likely born in the center, and give rise to the plateau observed in the X-ray afterglow when it is being spun down by the magnetic dipole. If the centrifugal force is insufficient to support its mass, this protomagnetar will collapse to a black hole, which may be responsible for a steep decay at the end of the plateau. By systematically analyzing the BAT-XRT light curves of all GRBs detected by swift. We characterize them into several groups based on how likely of the GRB being powered by magnetar central engine, and derived the parameters of magnetar, calculate the total energy to compare with energy budget of magnetar. Using the collapse time to constrain the equation of state (EOS) of NS for short GRBs