In this presentation, a class of modied weighted essentially non-oscillatory (MWENO) schemes is presented in the nite dierence framework for solving the hyperbolic conservation laws. These schemes adapt between the linear upwind scheme and the WENO scheme automatically by the usage of a new simple switching principle. The methodology to reconstruct numerical uxes for the MWENO schemes is split into two parts: if all extreme points of the reconstruction polynomial for numerical ux in the big spatial stencil are located outside of the stencil, the the numerical ux is approximated directly by the reconstruction polynomial, and the approximation is a linear and high order accuracy; otherwise the WENO procedure in ［G.-S. Jiang and C.-W. Shu, J. Comput. Phys., 126 (1996), 202-228］ is applied to reconstruct the numerical ux. The main advantage of these new MWENO schemes is their robustness and eciency comparing with the classical WENO schemes specied in ［G.-S. Jiang and C.-W. Shu, J. Comput. Phys., 126 (1996), 202-228］. The MWENO schemes can be applied to compute some extreme test cases such as the Sedov blast wave, the Leblanc and the high Mach number astrophysical jet problems et al. by using a normal CFL number without any further positivity preserving procedure for the purpose of controlling the concurrence of the negative density and pressure. Extensive numerical results are provided to illustrate the good performance of the MWENO schemes.