Two-dimensional numerical calculations using weighted essentially non-oscillatory schemes （WENO） scheme were performed to study velocity gradient in the Kelvin-Helmholtz （KH） instability for supersonic fluid. It is found that the velocity gradient has a stabilization effect on the KH instability for supersonic fluid, and the linear growth rate empirical formula with velocity gradient stabilization effect is deduced. The empirical formula with velocity gradient stabilization effect agrees well will the simulation results. The sharp density contour is obtained, which indicates that the WENO finite difference scheme has good capturing ability in interface deformation. The evolution of KH vortex is influenced by the velocity gradient. When the density gradient is fixed, it is found that the larger the velocity gradient the smaller the transverse scale of the KH vortex.