Properties of kinetic Alfvén waves in the vicinity of a magnetospheric substorm onsetwere investigated using simultaneous observations by THEMIS multiple probes in the near-Earth plasma sheet in the magnetotail.The observations indicate that in the vicinity of a substorm onset,kinetic Alfvén waves can be excited by the density gradient or ion velocity shear in the high-β plasma sheet (β=2μ0nT/B2,the ratio of plasma thermal pressure to magnetic pressure) within the near-Earth magnetotail.The kinetic Alfvén wave has a small spatial scale in the high-β plasma.The parallel electric field accompanying kinetic Alfvén waves accelerates the charged particles along the magnetic field.The kinetic Alfvén waves play an important role in the substorm trigger process,and possibly in the formation of a substorm current wedge.