Abstract: A magnetohydrodynamic simulation method is developed for shock interacting with rectangular density interface in a magnetic field. The method employs 3rd WENO scheme and mixed GLM method. With circular polarized Alfvén wave propagation test and rotated shock tube problem,the method is validated. Under conditions that Mach number of shock is 10 and ratio of density of cloud to ambient gas is 10,evolutions of shocked interface in different initial orientations and strengths of magnetic field are compared.It shows that magnetic field decreases vorticity formed on surface and reduces growth of hydrodynamic instabilities; Field influences acceleration and mixing rate of cloud; And field is greatly amplified in some regions behind shock when cloud is presented. It is also found that,due to sharp corner,evolution of rectangular interface is different from circular one.