The structure of plasma sheath in an oblique magnetic field is numerically investigated by using fluid dynamics method. The simulation results reveal that the magnetic field has significant effects on the plasma sheath. Especially, the ion density distribution near the sheath edge changes obviously. Two cases of ion incidence are considered here. The action states of ions are more complicated when the ions enter the sheath with an oblique incidence angle. Under suitable conditions, Lorentz force induces fluctuations in the ion density. Ions could gather in some regions.