There is a general consensus that the development of a thin current sheet in the Earth's magnetotail plays an important role in substorm initiation and dynamics. In this paper, we discuss one plausible connection between susbstorm current system and thin current sheet dynamics in the Earth's magnetotail. We present evidence that the main current in the substorm current system closes meridionally, with the substorm current wedge constituting only a weaker current loop. We propose that this entire substorm current system can be understood on the basis of current disruption associated with a kinetic plasma instability operating in a thin current sheet. The kinetic plasma instability produces magnetic field line slippage, leading to the dynamo action to drive an outward radial current in the azimuthal current loop. The magnetic field perturbation in the magnetosphere associated with this meridional current system is estimated. The possibility of magnetic field line slippage arising from magnetic reconnection in this azimuthal current system is also discussed.