A radio frequency flat plasma sheath model in an oblique magnetic field is built, which has one-dimensional coordinate space and three-dimensional speed space. The effect of magnetic field on the structure of radio frequency sheath and characteristic parameters are discussed. The numerical simulation results show that the effect of magnetic field on the sheath structure cannot be ignored. In particular, it brings about obvious changes in the ion density distribution and velocity distribution. Furthermore, the magnetic field cannot change the total energy density distribution of ions, but the Lorentz force does influence its movement state, and at the same time affects the ion energy distribution in every directions, as well as the incidence departure angle of ions.