In recent, nonlocal stability analyses of the cross-field current instability that may operate in the geomagnetic tail, it was found that the instability is suppressed when the cross-field ion flow is uniform but that the instability is restored only after a substantial velocity shear is introduced. However, the velocity shear also excites the Kelvin-Helmholtz instability. Therefore it is important to understand how the cross-field current instability and the shear-driven Kelvin-Helmholtz instability mutually interact and compete with the available free energy. As a first step, with the use of Hall-MHD, theory and two-dimensional simulation, this paper investigates the development of the Kelvin-Helmholtz instability for a thin current sheet with sheared velocity flow. It is found that a finite north-south field at the center of the neutral sheet inhibits the growth of the Kelvin-Helmhotz instability to some extent. However, the timescale of its growth is still sufficiently short, so that this instability may play a part in broadening the thin current sheet at the time of substorm expansion onset. ¿ American Geophysical Union 1996